You may have seen paintings advertised for sale at eBay or other internet auction sites that are painted on loose canvas. The seller will tell you it's less expensive to ship this way; they can roll the paintings up in a tube and ship them more economically (usually from another country). They might even try to sell you stretcher bars when you buy the painting for an additional cost. You need to be wary of sellers who do business like this. They are not independent artists and in most cases they are not gallery owners. Legitimate gallery owners don't even like to sell a painting without a FRAME, much less the stretcher bars. The fact is, properly stretched canvas needs to be applied to the stretcher bars before painting or shortly afterwards to be sure the paint surface dries at an even rate. Of course the ideal method is to stretch the canvas before painting on it and to apply three or four layers of primer (gesso). Folks, if this isn't done before painting or shortly afterwards you are asking for trouble in the form of a sagging painting a few years down the road. Prestretching the canvas- and yes, there is a very important procedure that needs to be followed so that this is done correctly, eliminates the possiblity of sagging and uneven drying. Unfortunately, by the time you observe this happening to your treasured work of art, the person who sold you the painting will be long gone or still iving in a third world country. You can avoid being taken advantage of by looking more closely at the auction before you click that "BID" button. Is the auction offered by an actual artist or gallery owner? How can you tell? Many artists, although not all, offer a certificate of authenticity along with their paintings. This certificate guarantees that the work was produced by the artist in question and there are no copyright issues. Sadly, today there are many sellers who will advertise a work as their own but the work was actually painted by someone in a sweatshop making 50 cents an hour. These type of paintings will not rise in value as the years pass and they may even fall apart within a few years time. Although they are probably fine for the buyer who is looking for something pretty to match their couch and who will want to change the painting next year when they buy new drapes. Discriminating collectors, who are interested in building an actual collection of fine art, will find more value in paintings and drawings that are listed by independent artists or galleries who will cheerfully provide them with an artist's biography and contact information.