Quoted from Beaumistim:
Someone puts a pin up for sale. I offer full asking price.... Never even get a response. Why do you even put it up? Even if you sold it already, take it down, maybe a reply of " it sold already".
To be fair, I live in an area where there is always chum in the water, and I haven't been into pins for THAT long, but so far I have never succeeded in buying a pin from a "For Sale" ad. I've been in second position by replying within 10 minutes of the ad being posted, and way off the back of the pack by replying within an hour.
By far my best luck has been with "wanted" ads, or by just letting my non-game friends know that I'm always looking.
It's definitely a seller's market right now.