The labels are used interchangeably and the firms behind them are not. A media buyer places advertising efficiently; an advertising agency makes the advertising; a marketing agency is supposed to decide what should be sold to whom and through what. Buying the wrong one for your problem is the commonest expensive mistake in this market.
Three different businesses under similar names
Media buying is bought on efficiency and scale, and its economics reward volume. Creative production is bought on craft and is priced per project. Marketing strategy and channel management is bought on judgement and is priced by time. A firm doing all three has an incentive to recommend the one it has capacity in, which is not a scandal but is a reason to know which you needed.
Match the supplier to the problem you actually have
If nobody knows who the customer is, you have a strategy problem and buying media will not solve it. If the offer works and you cannot reach enough people, you have a media problem. If people arrive and do not act, you have a creative or a product problem. Diagnose before shortlisting, and say the diagnosis out loud in the brief so proposals answer the same question.
Ask how the firm is paid on each part
Percentage-of-spend on media, project fees on creative and retainers on management have different incentives, and a blended monthly figure hides all three. Ask for the split, ask whether any media is bought on a principal basis where the agency owns the inventory and resells it, and ask for the rebate and commission position in writing. This is standard practice to ask and is often not volunteered.
Who owns what when it ends
Advertising accounts, creative source files, audience lists, tracking implementations and the analytics property should all be yours. Agree it at the start. The end of an agency relationship is when you discover whose name the assets are in, and it is far too late to negotiate then.
Questions people ask about digital marketing and advertising companies
Can one firm do all of it?
Yes, and many do it well. The point is to know which part you are buying and what each costs, so weakness in one is not hidden by the bundle.
Is percentage-of-spend a bad model?
It is fine at scale and poor at small budgets, where it cannot fund the work. Ask for a floor and a description of the hours it buys.
What is principal media buying?
When an agency buys inventory itself and resells it to you at a margin rather than acting as your agent. It is legal and disclosed in good practice, so ask.
How do I compare proposals that are structured differently?
Force them onto the same shape: media spend, management fee, production cost, and the named deliverables under each.