Im gonna 99% of they time, probably higher that inverts are not going to transfer anything to a tank.
Secondly if quarantining an invert there is no way to tell really what or if it is carrying anything and thirdly you have no way to treat even if you did, so then what?
Ive never had a problem with inverts carrying anything. Inverts i buy get a good looking over at the store and they acclimated to the tank when i get home. Obviously if i see something 'off' at the store then i wont buy it. Really your not going to be able to tell any different in a QT tank.
If you see something attached to a snail shell then it should be pretty easy to spot and not buy it. Ive seen aiptasia on snail shells and all kinds of things. Pretty much the initial inspection is the best prevention you can do in my opinion.
29g Mixed Reef, 150w 14k Phoenix MH w/ Moonlights, Reef Octopus BH1000 HOB Skimmer, Ecotech Vortech MP10es, ReefKeeper Lite (Plus), PH Probe, Temp Probe, ATO, Carbon/GFO Reactor.