It's not uncommon for studies to be funded by industry. It works like this: There is a limited amount of funding available for studies. Some small scale stuff gets done to identify opportunities. If one of these finds e.g. that milk potentially reduces hair loss (made up example), then the researchers will want to explore this further in a large scale trial, which needs a lot more funding.

Along comes the dairy industry, keen to support further research because it could help them sell more milk. On the other hand if the exploratory stuff showed hair loss caused by milk, then the dairy industry won't fund further studies, and chances are it won't get done at all because there is no one to fund it.

We shouldn't discount all industry funded studies because there's a good chance they are done properly, but we should treat them all with a grain of salt because of what is not studied. For example if milk reduces hair loss but also causes your toes to fall off, chances are we will only have the large scale study about reduced hair loss and people would discount the study about toes falling off because of it's small scale.

In this case it's a bit more clear cut. Does Roundup cause cancer or not. Lots of researchers will want to study it, but only the studies saying it doesn't will get funding from the manufacturer so this seems a lot clearer that we probably can't trust those studies alone.

This is why we need a lot more government funded science and research. That money is used to fund the studies that industry won't fund, to bring balance to the research. We could try to publicly fund all studies but I don't think that's achievable in the short to medium term.