IMO, a minimum post count shouldn't apply to members that want to buy. It should be geared more towards people that want to sell. Just to keep some honesty.
IM personal O...there are deals to be had from people that come on just to sell their stuff and get out of the hobby! If their prices are too high, they are usually 'blasted' by members and are given a reality check!
If we didn't allow them to post here, they'd be on Craigslist. Often these people have been on MR, but have not previously signed up/posted. I, myself, was 'lurking' for over a year before I signed on.
If you think/know of someone that is selling for a profit (stealth vendor) please report them, we'll keep an eye on them... our 'real' vendors support this site and are the reason the site and swaps are successful! For livestock and new equipment they should be your 'go to' people, whenever possible.