1. Buy a catalogue. You can get a fabulous Cigarette Card Catalogue for just £7.00 with free P&P from the London Cigarette Card Company. Their Trade Card Catalogue is even better value at £5.50 (that covers everything except tobacco product cards). These books will tell you when a set was issued, how many cards constitute a set, any printing variations or rare & valuable error cards to watch out for, and most importantly, an idea of price structure. Always handy to know if one card is worth ten times as much as another. If somebody on here is asking more than half the catalogue price for anything less than mint condition cards it's tantamount to robbery.
2. Beware of overgraded cards on here. eg good condition probably means fair at best. Poor condition cards will probably end up in your dustbin. Near mint generally means light wear.
3. Find honest and reliable sellers and stick to them. Big doesn't always mean brilliant.
4. Beware of mixed lots. A mixed lot of cigarette cards will probably contain at least 80% Wills and Players cards. That's fine as long as you don't have a huge Wills and Players collection already. If you're collecting tea cards, a mixed lot is probably 90% Brooke Bond.
5. Beware of cards in sleeves. Unless they're specifically advertised as brand new, the sleeves are probably old, worn and yellowed. You're paying extra postage to get the cards sent out to you in sleeves that you'll probably have to throw away and replace at your own expense later.
6. Know about snobbery. Especially if you're buying with an intention to sell on any surplus. Some people won't touch cigar, tea, confectionery, bubblegum or any other type of trade cards with a ten foot pole no matter how good they are. The same goes for stickers and transfers. There is also a very specialised and complicated market for overseas issues I'd advise you against involving yourself in as a beginner; anything with Chinese or Arabic writing on the back can be tough to identify, let alone sell. Cards with foreign or indeed English text that provide you with little or no means of identification are often BAT (British-American Tobacco) issues, but said firm were by no means the sole culprits in that department.
7. Know your themes. Unpopular, and therefore cheaper, themes include trees & flowers, do you knows, household / gardening hints, most kinds of wild animals, birds and fish, coats of arms, sectional / jigsaw sets, flags, scenic views. More desirable are film stars, TV shows, military, astronomy, science, engineering, history, royalty, sports of all kinds. Horses are strangely popular, as are cats. Dogs too sometimes, but there are a lot more dog sets around.
8. Ask questions of sellers. That's what the Q&A at the bottom of the item description page is for. A lot of incompetent and / or slapdash sellers on here. If they're attempting to mislead you by being vague or showing blurred photos it's the only way to flush them out. If they don't answer your question then don't buy!
9. Beware of reproduction (repro) sets. I collect these myself when they're cheap enough, but only because it means I can get a great set for £5.00 as opposed to paying £500 or not getting it at all. Read the small print. They don't always make it obvious that the set is repro. If it says mint condition full set and you've never seen the set before it's odds on a repro. Lots of sets that are very cheap anyway, such as Wills Railway Equipment, have been issued in repro form for no good reason.
10. Don't be impulsive. Be patient. Did you lose something you really wanted? Don't worry, chances are someone else will be selling one sometime soon and you'll get it for half the price.
Oh yeah, and it wouldn't hurt you to join my new group. It's called CARTOPHILIAC and I believe it's the only one of its kind on ebay right now. Let's learn from each other and pool our resources, eh...?
NB I have had 25 views on this guide in 5 days yet not one single person has hit the "yes" button to say it was of some use to them! Fortunately nobody has hit "no" either. I'm quite saddened by that. Voting does not commit you to anything and you will remain completely anonymous. All it does is get me a few brownie points in the eyes of ebay, so please, do me a favour and DO vote from now on. Not much to ask, is it...? I'm standing on my head to try and sell stuff on here with very little success and I need all the help I can get from you guys!