They are almost certainly MSDN keys. If you have an MSDN account you are given a number of keys to test environments etc. My accounts give 2x Windows 10 Pro for example (along with lots of others).
They are 100% retail keys, assuming they come from the MSDN. They are, however, not meant to be resold, so the seller is breaking their terms and conditions.
Once the key is activated with Microsoft, it will continue to work as a retail key. The only issue is if the key is not activated and the MSDN account is suspended, in this situation the key will not activate.