I used to work in a second hand watch shop as the in-house watch maker. Working on the movements day in day out certainly helps the buyers, I just had to open a watch to tell instantly on the really good fakes.
To the people talking about fake movements getting as good for less money, I can't see it being easily done myself.
For example the 'generic' wheels that cousins sell are very easily identified visually when stripping a watch, not talking about how often they are out of round and the pivots really poorly polished.
The finish and bevels on for example the pallet fork would be hard to replicate without serious investment in very very expensive custom made tools. Sure they could get close, but anyone who works on these movements regularly will be able to spot the differences.
It doesn't help the general public, but take the time piece to a trusted place who regularly works on the watches and they will be able to tell you.
As Haywood has said, take it to a standard watch reseller or agent and good luck, they may know less than you. Take it to a known expert or trusted watchmaker.