Smokers now a days are pariahs, but early in the century cigarette lighters were the necessity.  Early lighters were uliltitarian and somewhat unique for the smoking population.  Far too many were just thrown away.  A total waste of our history.  What are left can be found on eBay in various forms.  Estates, grandpas, expensive table lighters of quartz and leather, etc.
  I began collecting when I went through my old storage boxes.  There was my uncle's Ronsons case lighter from the 1920's when he sang in the old minstrels.  A lift arm lighter from the 1930's with the worn leather wraparound. My old Army Zippo lighter from the 1950's, (which they repaired free) for me.  A unique side action lighter from the 40's. Trench lighters from WW1, survival lighters from WW11. They are gold mines!
  All of these seemed too good to throw away.  So I began collecting more on eBay! Here is some advise for you:
    Concentrate on the old flint, wick and fluid lighters. The butanes are iffy and, at my 9,000 feet altitude, must be carefully bled of gas and refilled.
    Of the old fluid lighters, clear out the old 'soft' flint residue.  Use an unbent paper clip or drill bit  for this in the flint channel, otherwise the flint can't reach the striker wheel. The mechanism is quite simple. With a stiff brush, scrape the residue from the flint wheel.
    There are many brands, but the cream of the crop are Thorens of Switzerland, Braun of Austria, and the Rolls Royce from Switzerland, the Dunhill.  These bagan to appear in the 1950's and I call them the James Bond lighters of film.  They are usually gold plated and still sell for $500 new. Every collection must have at least one. You can still find some in 18K gold...a real keeper.
    Old lighters need a flint to spark.  The Dunhill lighters that I've found on eBay didn't have a flint.  It seems no one learned to replace them.  It is really simple. Open the top, slide the very top piece above the flint BACK, which flips out the flint holder, and insert a new one.  Many of these languish because nobody saved the instructions and that's a shame!  It doesn't take a rocket scientist to figure them out.
    Butane lighters began appearing in the late 50's and are a bit tempermental. Before, or upon receipt, they must be bled, to get the trapped air out of them.  Some of the early ones, like Colbbri, are collectible.  Most others are not and may be a waste of your money. I use an old empty butane refill, with a hole punched in the bottom, to bleed the lighters of gas. Works great every time and empties it..
    Lighters come in all shapes, and that is what I always search for.  The tiniest lighter.  A coin shaped lighter, like the French 5frank one; a musical lighter, a rolex., war lighters.  You name it.  Search and discover! It's usually there. Be patient. Search the eBay for one of the 20 lighter display cases and rotate your vintage lighters through it back onto Ebay.  It's a wonderful conversation piece for your home, often  profitable,  and a fun diversion.
    One last suggestion: get an old cigar box and save your sick lighters to canabalise. It's amazing how many parts are interchangeable!
    Zippo is a collectable make.  Learn more about the markings (slashes and dots) at the Zippo website.
   Of all the things on Ebay, nothing has been more rewarding and profitable than my vintage lighter collection.
    Good luck collecting and enjoying them. They just aren't made anymore!