" If he says that he can develop the webshop with no extra cost afterwards when it is finished" - in that instance, then indeed I would expect the developer to own up to all upgrades, maintenance, etc, etc. I can't believe a developer would say that very often, but if they did, then indeed they own the costs of operation. You buy a brand new car, you are entitled to a warranty. Just as with software, which if it's defective, they need to make it right. However, their software is not Magento. They didn't develop it, it's not theirs to own, not theirs to sell, not theirs to maintain unless agreed. You buy that new car, you have to put fuel in it, you have to put oil in it, you have to put air in the tyres and you have to change light bulbs that burn out. There are costs of operating a car that you as the driver must take on board. In much the same way, a web shop will need core software updates, possibly major version upgrades, it'll need hosting and of course new products added with photos and descriptions, plus marketing costs to promote it. Buying a webshop isn't a one and done scenario. You have to continue to pay for things to keep it going, otherwise it falls apart, just like a car. When you bought a car, they made abundantly clear the warranty. You know what's covered, what's not and for how many years and thousands of miles. Hopefully you used the same due diligence when buying your webshop, and you asked what's covered, what's not, for how long and at what cost. If you didn't ask for a warranty that covers everything, at no cost to you, then you didn't get a warranty like that.