Collecting antique maps can be great fun. As many come from atlases they have been protected for most of their lives. There are not many fakes about but there are reproduction maps. The most common is a series of John Speed maps printed on brownish paper to look like parchment. There are thousands of these around and I regularly get asked about them when they are found in an attic. If the paper looks brownish, mottled and like parchment, sometimes showing fold marks, the chances are it is a modern reproduction. I get telephone calls about these maps every other week when someone finds one in an attic or a garage. They are interesting but have no real monetary value.
If your Interest is British County maps then you will probably find my ongoing project to offer more information on the amazing cartographers whose works you might want to collect. Still in its infancy and a lot of work to do but please check it out.