I do not believe it is illegal to sell a used mattress under Georgia Law. I cannot say that it isn't a violation of Federal Law, however, I do not think that it is.
My question is, in this day of rampant bed bug scares, where would you find someone to buy a used mattress?

Ironman, where is this Antique Mall at? I checked one out today that sounds exactly like the one you are at except for the price was lower for a 10x10 (of course, the closer to the door, the higher the price).
I am seriusly considering doing this but I looked up this thread to check in with you to see if you are still making money and if you still recommended it.

Spoke to a couple of vendors while I was there and they were very enthusiastic. I am just concerned that I don't have $100-150 to give away if the merchandise isn't moving.

Your opinion would be appreciated

I had an old timer get mad at me one time when I told him I would have bid higher on the unit he just won but the stuff in the unit was really heavy (plumbing fixtures and other large items) and I just didn't want to move it. He got mad and said then why did I bid him up. I told him I didn't. I bid to what it was worth to me factoring in the physical labor involved. Kinda of ticked me off but what can you do.
If you do plan to bid up a regular, you better be careful in 1) he doesn't stick you with it and 2) he probably has more money than you and can take some losses in order to pay you back.
One old guy at an auction I went to about 6 months ago was buying every unit. After the first 4, one of the newbies decided enough was enough and tried to run him up. He wound up getting stuck (in my opinion) paying at least twice what the unit was worth.
The old guy bought 8 of the 10 units at an average of $600 a unit. He didn't look like he had a dime to his name. I stayed to make sure he had the cash. And he did...and a lot more.

THere are no minimum bidders. The storage facility, however, may have reserved the right to refuse any and all bids and may, therefore, reject your bid (in essence setting a reserve price). One of the first units I ever bought, I was the only one there. I offered $50.00 (It was a 10 x25 about 1/2 full) and the lady got really offended and refused the bid. I asked her what she thought was fiar and she said $150.00. I agreed. As we were walking back to the office several other people showed up and she asked me if I wanted to bid the unit again as maybe I could get it cheaper. I refused.
That was a great unit. I found a broken gold necklace that I sold for $500.00 (Wish I could have sold it now--gold is twice as high) and I still have about 5 really nice expenxive leather coats to sell.
So, bottom line is there is no minimum amount of people but even if you are the only one there, don't expect to get it for next to free unless it appears to be all junk.

 Personally, I would examine the safe and if it appeared to be in really good shape, I would pay to have it opened and keep it for myself (I could use one for rifles and other vaulables). If it did not appear to be worth keeping I would just break into it. I would not pay to have it opened hoping that I could break even (or profit) from selling it. Of course, you may not feel the same way.
As with all the other posters/lurkers, I can't wait to hear what you find inside.

You need to check you state laws on the ownership or sale of slot machines. In some states (most states) they are illegal to own or to sale. Some states have exemptions for machines made prior to a certain date.
You just need to be careful. Obviously if you keep it, your not likely to have the police show up at your door (assuming it is illegal in your state). However, advertsing it for sale may bring them down on you.

That is the hardest thing for me to do....sell for way less than I think it is worth just to turn over the inventory. However, it is something I am going to have to do as I have filled the space I rent to sell out of and my basement is full.
I passed on the first reasonably priced unit I have seen in months yesterday because the unit was full of large furniture and I had no where to put it. The leather couch was worth the sellng price by itself.
I believe that the more units you buy, the better the odds of hitting the big (or reasonable big) payday. However, you can't buy more stuff if you run out of room. Hopefully, I can stop looking at the money I feel I am losing by selling the stuff underpriced and convince myself to look at the money I am actually making and the potential income from the next unit.

I have had this idea recently too. I have been to about four local "merchandise" auctions trying to find a place to sell a truckload or so of items too inexpensive to sell on Craigslist. None of the auctions are convenient to my area of town and none of them were handling the used items (mostly food and the cheap new made in China stuff). So....I came up with the idea of starting one in my area.
Originally, I tried to get my brother in law to go to auction school to get his license but the schools are not convenient and the cost is around $1500.00 so he isn't likely to do it. I have a full time job so I don't have 2 weeks to go to auction school.
I am thinking of contacting one of the auction companies that run the merchadise sales and seeing if one of them would come run an auction in my area if I could locate a building.
What I would really like to do is get a building large enough to have a store on one side and an auction area on the other.
If any of this gets off the ground, I will post an update.