I've been using Trillian on my PC and my iPhone for ages, and it works perfectly. No native iPad app yet, but it works fine on the iPad in doublewide mode. I'm sure its just a short hop to a beefed up main version. Works with Jabber/Aim/MSN/ICQ/Gtalk and can even deal with twitter and email if you want it to.

If I run a grocery store, I'm allowed to say what kinds of checks I'll take.

If I run a coffee shop, I get to decide who'se posters stay on the bulletin board.

If I run an actual, physical auction house, I'm allowed to say "all payments run through the house." In fact that's what all physical auction houses DO say.

There's nothing "free as in speech" about a service like eBay. It's a commercial enterprise. They could demand payment in chickens and the ONLY right anyone has is to simply say no and not use them.