I am flipping a house that a previous owner smeared a bunch of concrete on a part of the basement wall. I assume they were trying to keep water from coming into the house but it didn't help.  I fixed the real problem but now I'm left with this ugly concrete patch on the basement wall.  I painted the wall but it still sticks out.  The biggest complaint that I get from buyers is this patch.  They are afraid that it is hiding something or there is a problem.  It is stuck tight and I can't remove it.  Any ideas what to do with this?

Skim over the entire wall. Tell buyers it was part of doing a external repair if they ask.

In the old days it used to be called sure wall.  Your big box store has it in a bag back by the concrete mixes.  it has short fiberglass hairs in it and used for back plastering concrete,,,,blocks,walls.  Use a bonding agent first.  Like Greg said do the whole wall if not ALL the inside walls.  An older concrete contractor is who I would call.  It looks white when done.

the first two posts are a great suggestion, just want to throw another option at you to consider, you can use a grinder with a concrete blade and use it like a sander and blend the batch into the original wall area to make the patch blend in better with the wall then use a basement paint like Drylock or a water proofing that is painted on the walls, its a little thicker then just concrete paint and will help to cover up the patched area.