F to S problem
Ascertained goods with description and knowledge of reasoning for usage. Market price changes thus, the market price rule applies!
Has F made it clear that F will manufacture the sheeting for both domestic and industrial use? If so, was the seller to the F knowledgeable and had a capacity to know better?
F did not understand the quality of the sheeting for 6 months. Is F in negligence or did a situation happened that led to this discovery?
Check the available market. (ask questions about place time and alternative competitors.)
After the conclusion; criticise the law and advise the client on what to do to avoid these kind of problems in the future.