As far as offering insurance plans for buyers is concerned, no, g2a doesn’t have any.
However, what they have is a customer protection program they called the Money Back Guarantee.
Let’s imagine a situation where you buy a key, it doesn’t work (let’s say it’s invalid, there’s a typo in it) and you contact the seller, and he or she doesn’t want to help you for some reason. It’s a highly unlikely scenario, but it is somewhat possible. There’s also a chance they won’t reply to your message within 7 days. If this happens, the MBG is also available to you.
So, what do you do? You file a money back guarantee claim, submit whatever details and documents are needed, and you’re done! All you got to do is wait for g2a to review your claim and if everything’s OK, you’ll get your money back.
Just make sure you don’t abuse the mbg (like, file a couple claims in a row) or else g2a can basically turn off this option for you.
Still, I doubt you’ll be forced to use this much (if at all, to be honest). Sellers are usually very helpful, so they’ll give you all the assistance you need.