Well, if someone is bumping up the price of something in the hope of conning someone out of their money, then I would happily snitch on them.
It's often said that you make your profit when you buy, not when you sell, so if someone has a shop and isn't making a profit then they're buying too high and it's pretty shabby charging excessive amounts to have someone else cover the cost of their mistakes.
If they're charging £100+ more than it takes to buy and import from AliExpress then dob away!