If it goes over the maximum due to heat build up, that's fine. The maximum is for cold pressure, not hot pressure.
The way I do it is to have a known good pressure guage and then check every so often to make sure the car's numbers are the same. If they aren't I will still know what the difference is. I don't trust any gauges at tire shops because you have no idea how many times they were dropped or when they were last calibrated.
Longacre Racing makes some good ones, which is what I use, but they're not inexpensive.