Indeed. Sounds good in principle, but how do you prevent someone from repeatedly returning items just to hurt a competitor and/or making frivolous defect/warranty claims against them?
Most fraudulent activity isn't attacking competitors, as it's prohibitively expensive, but instead propping up their own reputation. i.e. Amazon's fake reviews are mostly five-stars.
Very inexpensive. Especially when expensive products are involved + few competitors. The ROI is massively good.
Seems like a subset of the fake-review problem. Except with money exchanged, tangible costs to the retailer and more documentation.