Using browser exploits to steal commissions from affiliate links without even the user knowing. Let’s say you follow an affiliate link to a product and you go to checkout. When Honey pops up and tells you either that it found you a discount (or even if it pops up to tell you it didn’t find you anything) it secretly opens a new tab to the page which replaces the cookie in the browser that contains the code that identifies who to give the commission to. Instead of the person who gave you the link getting their commission, Honey gets it instead.
Then if you used PayPal checkout, they would also “find” you discounts but swap them out with lower ones and pocket the difference. For example you buy something for $10 and they find a 30% off coupon, but tell you it’s a 10% off coupon. You go to checkout with PayPal and they charge your card $9 but only pay the merchant $7 and pocket the other $2.
I mean you can and they probably will. Unless something is easy enough to make yourself in your garage there will always be a free market to expand into and then extinguish.