If you reject a match, WikiTree will create a new profile and mark it as a "rejected match" -- indicating that you have determined that these are different people who happen to look alike. If you don't have enough information to tell, you probably shouldn't be marking a rejected match -- creating an invalid rejected match will cause new headaches later on.
You don't have to accept or reject a match -- you can can also simply "skip" people in your gedcom. If you are uncertain about some possible matches on a particular branch of your tree, it would be best to skip that whole branch and import it later after you've done more investigation (for example, contacting the people responsible for the other profiles). I suggest skipping a whole branch because skipping individual profiles from a branch can leave you with a lot of unconnected profiles needing to be connected.