Quoted from shlockdoc:
Some people prefer to not have a record of selling prices. He said make an offer, I am sure 95% of the pinsiders know the range of a pins price. He said 1st real offer, makes it easier sometimes to make an offer without an asking price. He did not say the highest offer gets it, which negates the auction designation. Most of the complaining is from people who have no intention of buying.
If people are going to use Pinside as a vehicle to sell games than prices should be listed and discussed. Helps the hobby understand market value. Otherwise there's no benefit here to anyone but the seller and buyer...and that's what eBay, Mr. pinball and Craigslist are for.