I have read a helpful guide from "puck1pound" about collecting autographs and agree with almost everything he says BUT I feel obliged to respond:

There ARE  private collectors around like me who have over the years quietly visited auctions or purchased entire collections from life long collectors who did not want those inheriting the collection to be ripped off and or sell it for a quick buck. 

I met Mohamed Ali in 1986 when he came to visit someone someone I was working for at the time.  I had my photograph taken with him and he gave me a signed autograph and dated it.  I did not realise it at the time but that was the first of my collection.  It went into the loft for years until I got it out and had it framed when I came across the photo taken of him and I.  Obviously I would never sell it but its here to be shown to non believers.

Once I became interested in collecting I would and have paid well over the odds purely because I have wanted the item.  I have not had to consider any markup and how much I could sell it for.  I obtained Bing Crosby and a letter written in the 30's at an auction I saw advertised on the local TV. The son sold it at auction after his mother died and he found it.  Why not keep such an item to be passed on in the family? I paid about £125.00 but was prepared to pay £400.00!! After the auction I recorded on video the news of the items sold.  I have Ava Gardner, Steptoe and Son, Lucy Ball, Michael Cain and many others obtained from people who have known or worked for the individuals concerned.  Yet if I were to walk into a dealers shop he would not offer a good price for any of them purely because he is wanting to make a profit.  

I think a genuine collector will have anything from Eric Sykes to Tony Blair unless they specialise in a particular area.  I have some in my collection I did  not know who they were.  I  researched Dulcie Gray and Michael Dennison and then understood their life long love affair and marraige.  I did not know who Sally Ann Hodges was but then sought out a Dick Van Dyke when I found our she was Truly Scruptious in Chitty Chitty Bang Bang.

So I think there should be more empahsis on the collecting rather the the buying and selling.   I have sold on ebay in the past just to have a clear out really and expect I will again.  Lets remember there are genuine people out there who do not belong to any trade orgaisations.  Does every collector of fine art have a gallery?  Not everyone who drives a Bentley will belong to the Bentley Owners Club! 

Ask the seller the questions suggested by people like "puck1pound" and you should not come unstuck. Dare I say it, if you have bought a fake surely you will only know it when you go to sell it presumably for a profit.  That makes you a dealer rather than a collector.