Who does each one owe a duty to?
One client each, and the two clients want opposite things. A sell-side advisor is engaged by the owner and is trying to produce the highest achievable price on terms that survive to closing. A buy-side advisor is engaged by an acquirer and is trying to secure a specific asset at the lowest defensible price, ideally without an auction happening at all.
That is not a difference of emphasis. It is the entire design. A sell-side process is built to convert one asset into several simultaneous bidders. A buy-side process is built to convert several possible targets into one bilateral conversation. The first manufactures competition. The second dismantles it.
Both mandates are legitimate, and most transactions have both present. What causes trouble is an owner assuming that anyone using the phrase M&A advisory is doing the first job. The phrase covers both, and the engagement letter is where the difference is written down.
What are the workstreams, side by side?
The sell-side sequence is preparation, then a built buyer list, then a controlled timetable. Financials are normalized and stress tested, a quality of earnings report is commissioned before launch, materials are written, buyers are researched and qualified for financing, approaches are staged, and bids are held to a common date so that a second bidder exists when the first one negotiates.
The buy-side sequence is screening, then origination, then a bilateral approach. A thesis is set, a target universe is screened against it, owners are approached directly and often before they have decided to sell, and the work then shifts into valuation, structuring and confirmatory diligence on a single asset. The success condition is exclusivity. A buy-side advisor who delivers a target into a competitive auction has largely failed at the assignment.
The diligence work looks similar and is commissioned at opposite ends of the timeline. A sell-side quality of earnings report runs roughly $25,000 to $40,000 for a business with $3m to $10m of EBITDA and $50,000 to $75,000 above that, and it is bought before a buyer has a reason to disagree with it (CT Acquisitions, quality of earnings guide, June 2026). The buy-side version is bought after a letter of intent, and its purpose is to find the reason.
| Dimension | Sell-side mandate | Buy-side mandate |
|---|---|---|
| Client | The owner selling | The acquirer buying |
| Objective | Several bidders on one asset | Exclusivity on one target |
| Universe worked | A buyer list built once and approached in parallel | A target screen run continuously and approached one at a time |
| Quality of earnings | Commissioned before launch, about $25,000 to $40,000 at $3m to $10m of EBITDA | Commissioned after a letter of intent, to test the seller's numbers |
| Fee shape | Work fee plus a success fee falling with size, 5.5% average at $5m and 2.1% at $100m | Retainer plus a completion fee. No published series exists |
| What failure looks like | One bidder | A competitive auction |
“Every advisor will tell an owner they are on their side. The engagement letter says who pays, and the process design says what the fee is paid to produce. If neither of those points at competition, the advice is buy-side advice wearing a different label.”
How is each one paid?
Sell-side economics are published, in the sense that advisors survey each other. The structure is a work fee plus a success fee that falls as the price rises: an average of 5.5% on a $5m transaction, 3.7% on a $20m transaction and 2.1% on a $100m transaction, with wide dispersion at every size (Firmex, Global M&A Fee Guide, surveyed December 2023). Seventy-seven percent of advisors credit the work fee against the success fee (Axial, 2026 M&A Fee Guide, 331 responses collected in the second quarter of 2026, published 23 June 2026).
Buy-side economics are not published in any comparable form. No regulator, professional body or survey publishes a buy-side middle-market fee series as at August 2026. In practice the structures observed are a retainer plus a completion fee, sometimes with a reverse incentive that pays more when the purchase price is lower, and sometimes an annual mandate across a whole acquisition program rather than a single transaction. An owner cannot benchmark the other side's fee, and should assume it exists.
The asymmetry matters for one reason. A sell-side success fee rises with price, which aligns the advisor with the owner on the largest single variable and leaves the misalignment on whether to transact at all. A buy-side fee that rises with completion aligns the advisor with getting the deal done, which is a different pressure sitting on the other side of the table during the same negotiation.
Can one firm do both on the same deal?
Not on the same transaction without the conflict becoming the deal. A firm holding both mandates is being paid by the party trying to raise the price and by the party trying to lower it, and there is no disclosure that makes those two instructions compatible on a single negotiation.
Across different transactions it is ordinary and often useful. A firm that runs buy-side mandates knows what acquirers pay attention to, what their investment committees decline, and how quickly they can fund. That knowledge improves a sell-side buyer list. The line is per transaction, not per firm.
Where owners should look closely is a related arrangement: an advisor with a financing relationship to the acquirer, or with an economic interest in the buyer's capital stack. That is not the same conflict, and it is quieter. The question to ask is direct and answerable in one sentence. On this transaction, does the firm or any affiliate earn anything from any party other than us, before or after closing.
Which one does an owner actually need?
Sell-side, if the objective is price, and buy-side only if the business is the acquirer. The complication is that most owners meet the buy-side first. Sponsors closed 885 add-on acquisitions in the second quarter of 2026, about three-quarters of all buyout transactions, against 289 platform deals (PitchBook, Q2 2026 US PE Breakdown, 6 July 2026, as at 30 June 2026). Add-on programs are originated by direct approach, so the first call an owner receives is frequently from someone paid to buy the business without a process happening.
Taking that call is not a mistake. Answering it as though it were an offer is. An unsolicited approach establishes that at least one buyer exists and no more than that, and the price a single buyer names before there is any competition is the price at which they would prefer not to have any.
The useful test is simple. Ask what the person on the phone is paid to achieve, and by whom. If the answer is that they are paid on completion by the acquirer, they are doing their job properly, and the owner has learned that they need someone doing the opposite job.
As of August 2026
Sources: PitchBook, Q2 2026 US PE Breakdown, 6 July 2026, as at 30 June 2026, for add-on and platform counts; Firmex, Global M&A Fee Guide, surveyed December 2023, for sell-side success and work fees; Axial, 2026 M&A Fee Guide, 331 responses collected in the second quarter of 2026, published 23 June 2026, for the share of advisors crediting the work fee; CT Acquisitions, quality of earnings guide, June 2026, for cost bands by EBITDA size; Kreischer Miller, What Is a Quality of Earnings Report and Why Would I Need One, 17 June 2024, for the sell-side and buy-side purpose distinction. The description of mandate duties, workstream sequencing and conflict practice draws on our own mandate experience and on Kenneth Marks and others, Middle Market M&A. No published buy-side middle-market fee series exists as at August 2026, and no figure has been substituted for one.