Arrowheads are a tough subject when searching the Ebay pages. For the beginning collector I would suggest auctions that have a Guarantee of authenticity. My other suggestion for beginners is that you spend at least as much for educational materials in the first five years of collecting as you spend on artifacts.  Their are many fine books available on this subject. The information inside these books when applied properly is more valuable to your collection than a G-10 Clovis. Before you bid you should always read the sellers feedback, ask questions, and use your reference materials to study the peice . Is it made of the right type of material for the area where it was found?  For instance : A Pedernales point (a Texas type)  found in Texas and made of Mohogany Obsidian would probably not be a wise purchase. Know the flaking styles of the artifacts you are interested in.  For instance: If the peice is an Archaic type, then it should possess an Archaic style of flaking common to the type. If their is a picture of the crossection available, study it carefully. Most authentic peices have a lenticular crossection. If it has a flat crossection, and is of a uniform thickness from tip to tail, it may well have been knapped from a sawn  slab. Look closely at the surface of the peice. Many reproductions have been chemically patinated. In some cases if the pictures are good enough this can be detected. Many of the peices that have been chemically patinated will show a distinct lack of patination on the high flake ridges, as the chemicals tend to pool in the lower flake scars. Knowledge is the key. The more knowledge you gain , the more enjoyable collecting arrowheads will become. GOOD LUCK!