@thor you are likely cheaper than the stores _and_ seem to offer more support. you don't charge 69€ for the cartridge but the whole package.

it's the same as letting a garage change tires for you vs. doing it all yourself. if a tire change costs 40€ you aren't bad off, given that they are faster and have the liability if anything goes wrong. you have the work of selecting the right thing for his printer, and that's included in the price. he pays for the convenience.