Driver55er

My 99 e55 was running just fine. But, while my car was in for a number of things at a private shop, I had all four of my o2 sensors replaced as maintenance. I got these aftermarket Bosch o2s direct from the factory (I have a friend that works there). After install, the shop couldn't get the car running right and it started to throw codes. I'm not sure which ones. They started disconnecting the o2s and decided one of my rears was bad ?! They determined this by switching the two and having the code come on on the other side/bank. So they buy an oem (which Bosch makes for MB) and install. They still have issues and supposedly have their scanner go down. So, they send it to the dealer to clear the codes.
The dealer too has issues and says the other rear o2 is bad and they charge me for another new OEM o2 sensor. I talked to my friend at Bosch and they say their o2 sensors are 99.9% good and rarely have an issue with them.

Have any of you techs had issues with o2 sensor replacement like this?
Or, did they just hose me for sensors because I brought my own and they couldn't figure our how to clear the codes or are there issues with "aftermarket Bosch" o2 sensors. If they both made by Bosch what is the difference?