The two costco tire departments I know strictly said their tires or no service. I even asked about new tires for our BMW in 17" and they fumbled on manual on what size can be put on... and still give me hard time.

I used to bring my own tires and rims to them and they mount and balance... no more... which is why I bought my own tire machine and parked it in my uncle's shop. I use his balancer. Now I am even tempted to buy my own balancer... his keep going out of balance and is manual calibration... takes a bit of time... but I just don't like the idea that I have to calibrate that machine every time I go there.