The Fair = A machine that has definitely been used, possibly not kept up as well as others.Usual wear and tear for a well used machine, pin scratches, some dings in finish, some rubbing off of decals, but machine should work.You can try visiting your nearest BERNINA store to find out if they can help, you might get lucky and find an authorized BERNINA Technician that's been around forever and knows all about the older models.
Many times manuals are not with machines or are badly damaged.If you have the original manual, store it in a folder or envelope to keep it safe from oil stains from your machine.You can visit local shops that often carry old machines to see what local prices look like, and if there are any for sale like yours.Ask your friends that regularly go antiquing to help you look, too.Many of them were based on a Singer class 15 machine, and are commonly known as "Singer Clones" - read a bit more about them here. If your sewing machine looks a lot like these machines but has an off brand name, chances are you have a generic or clone machine.
The overall condition of your machine is one of the biggest factors in estimating a value.
Extensive damage to the finish like rubbed off decals, scratches from use, dings in the finish, possibly some surface rust.
Electrical cords may be frayed, and machine should work, but is not in top-notch running order.
Vintage home sewing machines are not "industrial", "heavy-duty", "industrial grade", "semi-industrial", nor are they manufactured to sew anything other than regular home sewing projects.
Be sure you understand the difference and know what you have!
If your machine is truly an antique (manufactured before 1900), or if you really want to be sure about the worth, you may want to hire an appraiser to value your machine.