Upon inspection, the seat cushion were found not to be upholstered. / Upon inspection, the seat cushions were not found to be upholstered.
In #1, the cushions are definitely not upholstered and the inspection revealed that fact.
In #2, the cushions were inspected. That is all we can say for sure. Perhaps the inspector failed to notice that they were upholstered. Perhaps they weren't upholstered.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.