I bought my car there (2015 S85)... the sales dude told me they bought $1M of them from Tesla for resale...according to him (who of course, would never had a reason to lie), they sell more used Teslas than any other dealer.
So I got a reasonable price, I thought, but holy cow, do not go in there expecting them to have a clue. They literally sent me out the door for a test drive with no sales dude, so if I wouldn't have had a test drive recently, I would have had no clue what I was doing. Also, not sure if the sales dude would have been useful...it's a different enough car, especially with AP, that I don't think someone who sells one every six months will be very educational. Also, although my ad said no mats, one key, and no book, it had mats, two keys, and some little tiny book.... YMMV.
They also acted like it was a big deal I wanted it charged... I was heading to San Antonio, I thought that was a pretty reasonable request
The dude that did my walk through had NO idea... didn't know what a frunk was, where the charge port was, how to activate it, etc, etc. He could make the lights flash, turn on the turn signals, and activate the brake lights. So know what you want to inspect before you go... they won't help you with that
On a user note, they have a snack bar there, and soda machines, but no wi-fi. Really? And it took FOR-FREAKING-EVER. I was there over 6 hours, between the charging, test drive, detailing, paperwork, etc, etc.
So... the service is what it is. They offered me a laughable amount for my trade-in, they didn't want to come down to what I thought was a good deal, but finally got within $500 of it, so I took it, but I was an inch away from walking away. It's like any used car dealer, I think.. you can't go in uneducated or unwilling to walk away, or else you'll pay a premium. The car is AWESOME, and they did a good job with the detailing, and finally got semi-close with a price, so I wouldn't have any huge issues buying from them again. I would definitely be buyer-beware on the trade-ins though... they offered me 13-15K for my 2014 Prius, which I sold two weeks later for $19K. Make sure you know what KBB is, and what you're willing to take (I had my brain at no less than 17K, and they were saying "middle of that range" for the Prius, sight unseen, and somehow, I think I wouldn't have gotten a good deal if they thought they had me trapped by my drive to Houston or desire for the Tesla... it would have been the "oh, there's a ding... maybe 13.1".)
So... if anyone is thinking of buying from them, I would suggest driving one first with someone who knows about them... an owner, the gallery, whatever. Don't make TDA your first Tesla experience