Ya the cheap grinders will change the temper of the saw chain and they literally are not able to be hand filed. The expensive automated grinders use high quality grinder wheels and also air cool the tooth as it's ground- keeps the temper for in field sharpening.
I much prefer to hand file my saws- I run chainsaws every day for work and sharpen saws every day ( I get the pleasure of removing lots of trees filled with nails
, fences, rocks and all kinds of hidden treasures!)
Most dealers use electric grinders and if they aren't setup properly or maintained properly they do an awful job.
Sounds like the OP got burned ! Don't send your saw in with a bar and chain on next time lol