In addition to fake fossils, there are also composite fossils out in the market. These are simply lots of fossil bits glued together.
Mosasaur Jaws - Simply lots of bones shards and Mosasaur teeth put together and "stamped" onto a sand and glue "Matrix".
Trilobite Plates - Artificial matrix with bits of real Trilobites and lots of resin.
Giant Dinosaur Teeth - Shards and sections of many Dinosaur (Spinosaurus, Tyrannosaurus, etc.) teeth put onto another and stuck together with putty.