All avid Beatles collectors who have collected for an extended time can usually can tell the difference between an original and fake or reproduction Beatle item, but when you first start out it is very difficult . My only and best advice is to do research on the particular item of your choice, the internet has a wealth of information on Beatles stuff and I have found that these web sites below will tell you all you need to know about any and all Beatles Collectables.
In reguard to Beatles signature items, Ebay is full of them and unfortunately most of which are non-genuine, it is always advisable to get some kind of authenticity done by an expert e.g. Perry Cox who is an Ebay Member, type Perry Cox in the Advanced search for sellers ,Frank Caiazzio or PSA/DNA. These experts offer quick opinions in a 24 hour period for a resonable price.
I have been burned a couple times with certain Beatles collectables and I have learnt the hard way that it pays to do your homework and when in doubt don't so then you can enjoy the wonderful hobby of collecting.
All the W's