I'm based in Europe but together with a partner I'm a buyer of small tech businesses. We have bought businesses so are credible and are always interested in buying more. We could pay $8m if an interesting business came along.
The issue is that a lot of smaller deals fall through, either because of unrealistic final price expectations by the seller or because some metric that is super important to the business was calculated and supplied in the wrong way (i.e. churn). Or there are issues in structuring the contract because the seller (or his legal advisor) "overengineers" the contract -- lawyers can and sometimes do end up killing deals.
As a buyer, if I pay you a $25k fee, you now have leverage over me. Because if the deal doesn't happen I'm out $25k. If I don't pay you anything you're incentivized to get the deal done and try and draft a balanced sale/purchase agreement that works for seller and buyer. That means both parties making concessions on terms. In my mind, that is healthy, because if we finalise the deal you're getting a bag of money.
Let's say there is a clause we just can't find each other on. No worries, we can jointly decide to walk away. If I paid you and you're not willing to budge, then I'm out $25k if I walk away. It doesn't keep the discussion balanced.
Add to that that some people might (in the end) be unsure whether they even want to sell or not, and you end up in a situation where it's all mostly uncertainty (for both parties) until the deal closes.