I think it's a good idea, though maybe it should not apply to everything, like mentioned previously, some people are not sure what to ask. Maybe if you post a high price, nobody will show interest in it.
I have not noticed this as of late. Almost all of the parts I've looked at recently in the parts for sale section had a price or said best offer or make offer. A few guys are parting out trucks and it would be impossible to list prices for ALL
parts on the truck if this was a mandatory rule.
If I sell a single part I will list what I want for it and post a link to a picture. All in all,
the swap meet is a great board and I like doing business with fellow bolters.