Ok here we go, i don't qt at all. I have/had in my tank ich, vermited snails, aiptasia, hydroids, asterinas, uhhh what else? Lots more I'm sure.
I believe a truly established healthy system should be able to handle these things with no problems. I do sell corals from time to time and don't tell people about pests (not that I would make any attempt to hide them either). I wouldnt sell anything that i noticed a pest on though.
The fact is that if your concerned about these pests then your gonna dip or qt the things you buy from me. If you don't and you get a pest then that is your fault.
My tank is close to 10 years old now and packed with live rock and pests just arent able to take hold. I believe its the new tanks with dry rock that get overrun with pests.
Well thats my opinion anyways, feel free to rip me apart if you'd like!