Gresham's law is about (physical) currencies though - while it could arguably be somewhat extended to consumer products, the latter can typically be distinguished readily on more than just their superficial appearance. The fact that it's hard to accurately do so at point of purchase for most consumers is definitely part of the problem though.

Believe the Market for Lemons may apply:

[1] https://en.wikipedia.org/wiki/The_Market_for_Lemons