You can be sued if:1) You don't do what you contracted to do--e.g. violate the specifications or contract.2) You ignored the customer's instructions as to what they wanted.3) The site you built does not work (e.g. any shopping cart feature will not take orders; any "contact us" feature does not put the customer in contact with the business).4) You lied to the customer (committed fraud) about your capacity or ability to do what they wanted.That is not the situation you describe: if you in fact "do everything I say I am going to do but the buyer is still unhappy," they cannot sue you on any of the above grounds: their "happiness" is not relevant (UNLESS the contract with the customer states in writing that "satisfaction is guaranteed" or something like that, in which case you making their happiness relevant and guarantying it). If you comply with and do everything promised, then the only ground to sue you would be if your work is "unprofessionally negligent"--so bad that it is commercially unacceptable.If there are grounds to sue you, they could sue for the greater of what they paid or what your error or violation cost them. For example, say that you build a shopping cart which does not work and they can prove they lost a $3,000 sale which cost them $1,500 in profit: they could sue for the $1,500.