If someone is parting out a truck, and says "Part out truck, send me a list of your needs or call or....." then no, I don't think anybody would expect them to post prices.
If someone doesn't know what something is worth, how about "Make offer"?
But even then, if someone is selling something (gas tank, transmission, set of wheels) and they say "Make offer," they have a price in mind. Don't think so? For sale: 4Spd manaul trans. Good synchros, granny low. Make offer.
Now go ahead and offer the guy $25 for it. He isn't going to sell it for $25. Chances are, he has an idea of what he wants to move it.
Obviously, if someone is trying to get something out of their shop, or has decided something is for sale, 99 out of 100 times they now how much they want for it. For the 1 percent that doesn't, I think people would understand a post that says "I've got this, I don't know what it's worth, taking reasonable offers." Or, how about a post on the general page saying "What's the going price for this?"
If it were me, I'd put a post up that all ads must include a price or discussion of the price. If it doesn't, it gets deleted. Like a trip to the dentist, it'll be painful for some for a little while, but in the long run, it'll be nice.
