I got PSS as well. I have a tire gauge to make sure the PSI is always right. With my new wheels I didn't get new TMPS sensors and didn't want to use the stock ones since they'd be 50/50 reliability with new wheels so my light is always on, but I don't care, the tire gauge is all I need
I got mine filled up at the shop that does the work on my Z, besides them I don't trust anyone else (dealers etc...). If you have to have it done by someone that you don't know personally, always double check to make sure the **** is done right.