The charity idea's a good idea.
But if I remember correctly selling auto parts in public is against the law, and if it were up to me I'd think this would be too much extra work the mods/volunteers/admins would have to put together on top of whatever they already have to do.
There's already a Buy and Sell on Revscene that's pretty good enough imo
And it doesn't even charge you to use it. You can donate $5 to a charity of your choice after selling an item if you're in for charity.
Just my two cents.