Try a very simple test. Ask your Polish translator to translate this phrase “I have read and understood these terms.” and specify that you want to differentiate between a feminine/masculine gender in verbs.
If your Polish translator provides you with:”Przeczytałem/-am i zrozumiałem/-am niniejsze warunki.” then I am afraid he/she is not up to scratch.
Can you tell why? If you are curious, email me at maja(at)mylingua.pl for an explanation.