Well, I'm guessing with "auto tranny" you don't have a type s, so 275 sounds about average for an install. Was the other place a custom shop? Usually custom shops charge more for labor but you get a prettier install. As for the etiquette part, you should expect a written estimate before any work is started. Also the installer should discuss with you what you want done, mounting locations and all. See if the shop does appointments, if so it's usually better than just randomly showing up since if they're busy you won't be dissapointed for wasting time coming. As for the hovering thing, that's a personal issue. Ask the installer if he minds if you watch, and go from there. Some people can get nervous being watched while they work and that can cause them to either to take a very long time or worse make them jittery which can lead to damage. Hope it all goes well.