How can you tell if fillers are being watered down by injector?

Thank you for your question and I'm sorry that you're not satisfied with your results. Fillers typically come pre-packaged, so diluting filler is unlikely. However, if you are concerned, I suggest discussing your concerns with your injector. Otherwise, be sure to see a reputable provider in your area. 

Your injector should always open the package for the syringe in front of you. All legitimate fillers come sealed in a sterile package. If your injector opens it in front of you then there is no way they could have tampered with it. There is the other issue however of whether you should trust someone to put needles in your face if you think they are crooked enough to tamper with the Filler. You have to question whether they are cutting corners in other ways that might affect your safety. 

This is an excellent question.  Unfortunately, there is no reliable way to know whether your injector is watering down the fillers so it is best to see a board certified physician with excellent reviews. I have heard horrific stories of injectors overdiluting fillers, so please choose carefully.  You need a safe and effective treatment with a well qualified doctor.  This is the best way forward.