Todd is right - repro cards are often made up completely of reproduction items apart from the actual figure itself (the weapon may be legit but 9 times out of 10 it isn't. These are pretty obvious when in hand - often the card is thicker, the printing is different and on the whole they have a 'newer' feel to them. To be on the safe side, I would recommend buying some very cheap MOCs or even card backs when you start out so that you can get a feel for them
Re-seals are a whole different ball game - these are often all original parts (although a few repro weapons can sneak in and are a bit harder to tell. As a rule they are bubbles that have come away from the card - either by force or by age and then have been glued back down. The easiest way to tell is to check if the 'waffle pattern' goes all the way around and that there is no glue residue. Again these should be easier to see in hand than on pictures
The best advise I can give you is to start at the lower end of the scale and get familiar with the cards. Buying from the forums will also decrease your chances of picking up re-seals/repro as they guys have reputations to uphold and are not the sort of scum you find on eBay
