Good comments from other 2 guys.

I don't know if you are new to hairpieces. I have been wearing for over 10 years so when I get a new piece, I know if density is too thick or front hairline ends too abruptly (wall of hair as others described it).

There is no question that some are better made than others. I guess some factory workers are more skilled. Sometimes I get a piece that's just not right and I don't bother cutting it in because I know that would be a waste of time. If density is slightly too high, I pull out some hair with tweezers (before cutting off front lace) and cut some front hair to create "baby hair".

If you are not sure because you have not gone through enough pieces, I would try Paul's advices first.