Some stuff people have been doing on this site is stupid and doesn't make me want to buy any invites/accounts from you. So listen up.

DO have a messenger account.
Countless times I've wanted to buy an invite and this person says "we'll do it over PM". No. Over PM, I can't tell if you're screwing me over or not. On IM, it establishes a true "instant" version of messaging so I don't have to sit there waiting nervous. I expect you to respond quickly over IM.

DO post that messenger account on your thread.
It makes everything faster. Just do it. You won't get that much spam compared to the amount of sales you'll get.

DON'T be a dick.
Seriously, just don't. I hate it when sellers pester me with five pms before I've even gotten to my computer. Don't expect an answer either, I don't have to respond to you. Screw off!

DO be willing to lower your price.
Why the hell should I deal with you if you won't lower your price? It's a tracker invite! Just be willing to negotiate.

DO learn proper English.
Seriously? I can't fucking communicate with you if you talk like a monkey. Not to be insensitive, but do learn.

That's all I can think of atm.