You should just ask if they are familiar mounting with the binding you bought.
If they sell it themselves then you should be confident. If they don't sell that binding or that binding make, then you should be less confident.
They will ask you to fill out the standard rental/service form to set the DIN and bring a boot (for verifying BSL and final testing).
You can also mount on your first trip at a shop during your first trip up to the mountains (tahoe? where are you going?) .
If you're going up early season, many of the shops won't be so busy, so they can get it done for you by next day with perhaps only a small extra rush fee. They may let you take out a rental for reduced cost for the day.
There are plenty of respected shops up in tahoe that will do a great job.
Just based on volume they have way more experience. Tthink about the turnover in the rental fleet, and all the practice the techs get in setting up all those skis as well as testing the fleet. They get good pretty fast.
Edited by raytseng - 11/13/14 at 10:54pm