I have had a terrible time finding a processer that does a good job. The ones that are really good have a waiting list of at least a year. One we used a couple of years ago, the meat came back tainted. My mom was a meat cutter and she said if there is any problem with the cooling procedure (not enough room for the air to circulate in the cooler, for instance), it will go into the fat. So the hamburger did not smell good when it was cooking.
One thing I know for sure, never take beef into a plant that also cuts wild game during hunting season.
I just had a couple done and the lady at the butcher shop told me that they don't want them hanging long b/c the cooler didn't have enough air circulating. I usually have them hung for 3 weeks but she said no way that the hamburger would taste and smell bad.