Get them to use some bead sealer when they fit the tyres; it's often a horrible black gloop, but it's worked a treat on my old alloys on my V70; the tyres held their pressure for most of the time it's been parked up, dropping about 10psi over 2 and a bit years.
The places are reluctant to use it because they have to pay for it, but it's a good fix.
My alloys went around the bead, and even with being rubbed down they wouldn't seal unless I did a full refurb on them. Bear in mind the car had about 200,000 on it at this time.
Second on checking the valve... I discovered the core was loose on the wheel barrow and that was why it kept going flat!
Good luck!