Ask your contractor for the warranty certificate which comes with the product. It will have the name of the manufacturer and you can call and ask where a showroom is that has a sample of the product which you can inspect. If the contractor cannot produce the certificate, then ask him to direct you to the wholesaler or manufacturer where he bought the product, so that you can go get your own warranty certificate. Also have him to write in his contract or invoice the brand name and that they are argon filled. This way if something doesn't check out, you have something to use for recourse or for reporting to the Better Business Bureau if that becomes necessary.