Published lists of business to business agencies are assembled from directories, paid placements and self-nomination, and almost none of the entries were examined against your situation. A shortlist is more useful than a list, and building one takes an afternoon if you start from the constraint rather than from names.
Start from your constraint, not from names
Is the problem that nobody knows you exist, that people find you and do not enquire, that enquiries do not convert, or that customers do not stay? Each points at a different kind of supplier. A list of agencies cannot answer that and a wrong diagnosis makes every subsequent choice worse, so it is worth an hour before any names are collected.
Filter on motion and sector, in that order
Self serve and enterprise sales motions need different suppliers, and regulated or technical sectors need firms who have worked inside those constraints. Those two filters usually reduce a long list to a handful. Size, awards and location rarely change the answer and are what most published lists sort by.
Where credible candidates actually come from
Peers in your sector who have used the firm, the agency behind work you have admired, and the people who wrote content that genuinely helped you. Each of those is a stronger signal than a directory position, which is usually a function of who paid or who nominated themselves.
Make the proposals comparable
Same brief, same information, same questions, same window, and a stated budget range. Withholding the budget produces proposals aimed at the wrong scale. Three or four serious candidates is the right number; more and the pitches blur and the decision drifts toward whoever presented most confidently.
Questions people ask about b2b marketing companies list
Are agency directories useless?
They are useful for discovering names and unreliable as a ranking, because position usually reflects payment or self-nomination rather than an assessment of fit.
How many agencies should I approach?
Three or four that pass your filters. A longer process rewards firms with proposal teams rather than firms that suit the work.
Should I state the budget?
Yes, as a range. It is the single most useful thing in a brief and it makes proposals comparable rather than aimed at different scales.