I think T-Mobile is a great phone company for the price and very helpful, but here's my story at this location.
I got a OnePlus 3 which required a new nano-SIM card. In the past, I received a new card for free, but these guys told me it would be $20. The rep I was with told me I could call T-Mobile to cover it, so I did. The rep I talked to said this store should be able take care of it, but they would cover it anyways since I've been with Tmo for 16 years!
The rep at this store still made me pay for the card even though T-Mo support said they were covering it. He said that I received a credit to cover it but the difference was around $4.50. This location need to figure out how to work with corporate in situations like this.
The GM needs to know this is an issue and stop training his employees to be so aggressive towards customers.