I have not looked at gone broker in a long time so I'll take your word that they have 25 Model 18s priced too high for the market that existed before this economic depression. I do not think can learn much from that.

Over the last twenty years I've observed that similar vintage 18s and 17s in the same condition sell for the same price. There are more 17s but most buyers prefer 6" barrels. In the 5 or 6 years prior to this one top store price in my area for both was $700 plus tax for excellent condition examples. The $625 price you saw was reasonable for that time period. Rumor has it modern self defense pistols are selling fast so the store owner likely is not hungry. However they might be better off getting their capital in more of those fast selling case flingers. It's up to you to show them some pictures of dead presidents and see what happens.