Patrice, your post sparked an idea. Why not carry a needle and thread in your purse so you can test the sheet on the spot. Carry it in a pill bottle that can be easily located among the items we carry.(I hesitated to call it clutter, but then I would be speaking of my own purse.)
Now, are you speaking of new sheets, or used ones? I have found some really good buys at thrift store. Goodwill has gotten higher in price, spending $8. for a Queen flat is outrageous when others charge $2. I do not live close to a Salvation Army, but some of the AMVETS thrifts are very reasonable.
Again, "machine sewing" is a key...as well as "thrift" for quilts being given to charitie, and especially the homeless. They will be given a real test as they will probably not see a washing machine....unless someone offers to do them free.