Leak???

My husband and I bought a used 58 gallon tank setup from a local store here. We've had it set up since Monday, and haven't had any problems with it. I was looking at it tonight And noticed a water trail from the top corner. It seems to be a small leak, and my husband said he noticed the same thing the other day. Not a huge deal at this point to drain a bit of water because all we have is sand and live rock right now. Is this an easy fix? Obviously I'm going to call the store tomorrow as they guaranteed it was fine, but I'm just curious as to what potential fixes are. Thanks for the help in advance!

 

How full was the tank? Is it rimless or does it have a black plastic rim? I had what I thought was a leak. However, it turned out to be water wicking over the edge between the glass and the plastic.

 

I agree here make sure its a leak. Most leaks don't happen at top near rim, because there is not much water pressure. I would wipe it off and see if it come right back or slowly.