There could be various legitimate reasons, though.
The brand could be overstocked in a particular item and want to get rid of inventory without harming their brand cachet - you're probably not going to find a clearance section on Gucci's website, but that doesn't mean they don't have a need for it.
This is true. But why would they have an overstock? Either it is unpopular and not worth counterfeiting or it’s counterfeited immediately because it’s popular to undercut. The scenarios seem difficult to distinguish.
The consumer looking it up on Amazon isn't going to know which of those two scenarios it is. Thus, my point - blaming the consumer for purchasing it is unfair. There are legitimate reasons for a consumer to think the product is a) real and b) cheaper than usual.