Was I just sold a used cassette?
In all likelihood, the cassette is new.  The cassette is manufactured this way. The difference in teeth shape and depth is to assist the chain take-up when you change gears.
Look for wear marks on the ramps and grime between the cogs - a new cassette should be clean with no marks.  While it could be possible to clean a used cassette to 'new' condition, (likely more expensive than a new cassette), it would be next to impossible to remove wear marks off the ramps.