What if the tile work had proceeded as contracted and looked good, but STR refused to pay, saying it didn't meet their personal satisfaction (even though the contract didn't mention this option).
Could STR refuse to pay?

This scenario refers to a contract between a school (Northeast Independent School District in Bexar County, Texas) and a private constructor (STR Constructors, Ltd.). After obtaining the contract STR subcontracted Newman Tile, Inc. (NTI) for placing tiles in a kitchen. After several problems, STR refused to pay for NTI's work, and several reasons were presented before for not paying it.

Now we are asked about STR not wanting to pay because it doesn't meet their personal satisfaction, even though that wasn't included in the contract.

Well, STR cannot refuse to pay because their personal opinion was not included in the contract, and the general rule for this type of work to be considered properly finished is that a reasonable person would determine that the work was done correctly.

If it depended on the client's personal opinion, a lot of work would be considered defective just to avoid paying for it.