What should service provider do in case of relock

Dear forum users and colleagues

Lets disscuss what responsibility should supplier or the one who provided the service take if any IMEI stated done by official service relocks.

I write this mainly because this happened to me recently and the guy who did the unlocking took no responsibility and I had to unlock the phone again from my pocket. But the fact is that at that moment that service was advertised official T-Mobile premium service(not WW, which I was inclined not to believe but as I respect that guy I ordered it).

Please share your thoughts. Should it be a common rule for forum members or not?