What determines a contract breach from a bad job?

We learned in class this week that in some cases a party has more to gain from breaching a contract than upholding it. However, it may also be the case that a party does not entirely for go a contract while also not meeting the expectations of those they entered the contract with. For example, what might happen if I were to order a dress for an event, to later discover the stitch work is crooked and unattractive. At what point do cut corners make for a breach? How may this be determined?