There is only one way to distinguish legitimate good companies from bad companies - consider the fee given to writers.
US Companies should pay a minimum of 10 dollars per page
UK Companies should pay a minimum of 10 pounds per page
European companies should pay a minimum of 10 euros per page
and so on...
This means a pay rate of 40 dollars/ 40 pounds/40 euros etc. per 1000 words would be standard as given by legitimate US/UK/European companies. of course some companies pay more and some pay less but writers should stress on this standardization so that they are not exploited.
If you are a writer and work for less, you are harming yourself and others and also lowering the standards of the industry and encouraging fraud