I have been collecting, buying, trading, and selling sports cards for 21 years.
I can tell you that the best way to make the most money is the hard way, sorting through them, organizing them, and selling individually or as lots.
I have a collection of at least a million cards. I have enough boxes and totes that fill our 6'x6'x8' storage closet and then some.
Sports card dealers will offer you crap prices usually, unless you have high dollar cards. They will want to pick through and only get the best cards, since they have to sale them as quick as possible.
eBay has too many cards listed. Unless you have something hot, its not going to do great. I just checked eBay and there are 4,517,061 listings for sports cards. As far as doing Dutch auctions or grab bags, be ready to get 1 negative feedback for every 2 or 3 positive. You will get negative or neutral feedback for not giving someone what they wanted. Some people think that a $3 grab back should have a Cam Newton auto (for you younger guys) or a Mantle rookie (for the older guys). I don’t think I have ever seen 100% positive for people who offer grab bags, especially now when a seller has no recourse action to take. That is why you do not see as many of the grab bags. You can try to do the by the pound sales, but make sure that you toss in at least 1 excellent card of the buyers favorite player or sport in there. I am not saying to sort through the cards for these, just toss it in the mix to make dang sure they get at least one good card.
Card show booths are usually only good for guys with massive collections or stores, unless you are going to a small town. If you do not have good cards, people will not want to look through any of them.
The best place I have had luck at was at the flea and yard sale. After you get your cards organized by sport and category the best you can, get a subscription to Beckett online price guides. Each sport costs $7 per month, unless you buy a total access package for $24 a month. What I do is get a subscription for the main sports I want to sell and only the month I want it for. While I have the subscription, I price as many cards as I can and do live pricing at the sales.
I put a sign on my table that says "Sports Cards - Most 50% off Beckett Value". I use that as a starting price and let the buyer haggle from there. Some cards bring a premium, like Texas sports teams, my personal collection, highly sought after cards.
If you are going to sell your cards individually, you must know what you have and what its worth. As a collector, it is a major turn off to see someone ask $20 for a card that will only bring a couple of bucks. If you do not have an idea of prices, you need a quick way to price them, at current prices.
If you do not know prices, you can do one of two things. You will either drive customers away, or get yourself ripped off. Either way, it is a major loss.
There are a lot of worthless cards that I use for fodder. Those are the mass produced cards of the late 80’s through the late 90’s. Most of those years only have a couple of cards worth something that will sell. If it is not a card worth over a couple dollars, I use them as free giveaways with purchases of good cards. People love getting stuff for free, plus you get rid of your crap cards for free. Also, the free cards get buyers to look through cards again, and knowing that with every say, $15, they get a couple of free cards. That drives them to buy more cards, especially if it is a parent with kids.
Another point is to have a variety of cards, and make sure there are some awesome cards mixed in. You need to have a variety of game used, autos, game used cards with autos, short printed cards, rookies of major stars old and new, and a lot of inserts.
The sports card industry is still vibrant, but not like what you think. It used to be kids buying and collecting cards. Now, it is us kids that have grown up that are doing the collecting. Keeping that in mind, we do not just buy cards to buy cards, we want specific players, cards, years, etc.
When there is anyone around here that has boxes of cards that they do not want to go through, I will take a quick glance through the cards, and if I see something I like, I will make an offer. I love to buy boxes of cards just to see what I can find. I have a lot of bulk packed boxes that I still go through a lot of times and find cards that I did not know what in there. When I look on craigslist for card collection, I look at the pics.
I have some rules I go by if I am looking on Craigslist for cards:
1. I look for the years they collected and years they have the cards listed as. If they are crap years, I do not even respond.
2. If someone says they have a couple thousand cards listed for $200 and up, and they have pictures of boxes with just the tops laid open, I walk away.
3. Most small collections, unless they are pre-1980 or post-2000, are not worth looking at.
4. If the collection is 1990 and up, and they do not post a single auto or game used card, then its not worth looking at.
With all of that said, you have to remember, I do not just collect cards, I sell them too. It takes a lot of man hours to sort through and organize cards, so I won’t just throw money at a collection unless I know it will be profitable.
I can go on and on about this subject. If anyone has questions, I will answer the best I can. I am following this thread, so either ask here or pm me.