Its actually for us to get to know you.The 50 post rule does suck, but I also get it and how it may be used to prevent bots.
The classifieds are a perk of active membership at its core. Folks buy/sell here vs other sites because there is a level of trust and comfort. You have an idea who you are dealing with. Not some rando thats gonna show up and try to shank you and take your stuff or cash. Hell, I think in all of my deals only 1 lasted less than 15 minutes. There is almost always some socializing after the trade.
Heck, Ive actually shipped small items first and told the buyer to send me a money order. Because I trusted them due to their tenure here. I knew they were a respected long time member and I could trust their word. It doesnt happen often, but it has in the past.
Are there folks who just show up and pay the fee and pay to play? Sure. And those folks might not be as successful for the above reasons.