I think if you pay a fair price then the main factor will be time. Had I kept hold of many coins until today, I would have turned a nice profit on almost all of them. However I wanted the money to buy other coins at the time and didn't. Dealers sell for a profit so are going to want to buy at a discount to the current market value. Wait a few years for the market price to go up and the dealer's offer will approach (and hopefully exceed) what you paid. Sell too soon however ... OK, rarities are a shortcut in that if someone really wants something that rarely comes on the market they will have to pay the asking price. But in the end there's always a risk. The only way to hedge against it is to know your stuff so you don't pay too much and buy what you like in the hope that others will like it too. Personally I wouldn't rush into it. Decide what you like and do some homework. In every coin series there are gaps that are difficult if not near impossible to fill. And when that time comes you will have to pay for the pleasure, so it's always handy to have a 'war chest' for when that coin appears. But knowing which are the really tricky coins to find, and which just take patience, isn't something that can be picked up overnight. If it was, I personally think it would take some of the fun out of collecting! Though you can learn some of it from other collectors - I think that kept me going for about five years, before I started to get a feel for which coins can be found in decent condition and which are almost invariably poor, making better examples particularly desirable. And I'm still learning! Part of the fun is the chase.When I do get something that I really want I'm like a dog with two Di***