How to know what supplier is legit and safe.

Ive been on mounjaro a while and with the price hike I'm looking at reta. I'm not looking for any supplier recommendations, I just have a few concerns and want to know best practices on choosing one that is reputable, safe to use and is pure. I've seen some suppliers have a lab certificates but how do you know this is real, is there a way to check? and even if the test is real, that what you receive is from the same batch that was actually tested ?

Any advice welcome thanks :-)