You'll notice most of the responses are from Americans. They have it good, with numerous places to obtain items when they come out. It's easy for them to say 'never pre-order that far in advance from Ebay', and their advice is sound, but in many countries, like mine and possibly yours, there isn't much choice or options. ABC and Goodshipped are reliable. You shouldn't encounter too many problems, and if you do they'll fix them. I have no problem placing orders with either of them.
The idea is that if you pre-order you get it at the pre-order discount price. After their pre-order quota is full they normally raise the price. It started out that way, but these days it doesn't seem to make too much difference.
I have had a couple of problems with figures from this bloke. One was a figure arrived with two sets of the same hands. He said he would send me the correct ones, but never did. The other was a pre-order for the Mark 3 Ironman. When it hadn't shown up a year later I had all sorts of problems getting him to respond to my emails. Eventually he did, but he stalled me for three months saying April, then May, then two weeks time. All this time I had been asking for my money back if he didn't have one in stock to send me. When I finally did get a parcel it was the Mark 2. So it cost me to return it, and I'm still out a Mark 3. Ordered one from ABC, so I'm covered. His English is lousy so communications can be difficult. I'll never order from him again.
I'm not saying he wont come through for you, just that some are better than others. If you haven't gone over the 45 day limit you can start a claim through Paypal, and if you have you may still be able to go through your credit card, if you paid Paypal via your credit card that is.