Note how much trouble the Concrete Cow folks have gone to to eliminate the scrum effect round their sign-ups tables, because it's hostile and intimidating for some people. And for that matter, I don't find scrums that scary, but I do find them annoying and unpleasant, which means that I just walk away and don't buy anything.
If I ever took everything I had to a B&B stand, I'd need my own 12 foot table and a Transit to get it all there! And probably the ability to take credit cards (as there would be a copy of Ringworld at least) 😀
Ebay sold listings (search the item, scroll down the page and in the left side bar there's a option to look at sold listings (or completed which may be buy it now). Don't forget to search worldwide as well.
For board games, check ebay, but also BoardGameGeek. If you search the board game, once you've found the right one, go to the overview tab, scroll down a bit, and towards the right of the page you'll see the BGG marketplace data, and a link to price history just at the bottom of that section.
I usually price at around 50%-75% of recent sale prices, depending on condition (and completeness).
Note it helps to check BGG for board game manifests - I had to pull a handful of games from my list because they were missing critical components.
I logged 755 items: 186 RPG, 440 books and 129 boardgames. All the RPGs, 410 books and 74 boardgames (a lot of small games) made it into the car. I sold 55 (might actually be 56) RPG, 95 (might actually be 96) books and 14 boardgames. (I had a discrepancy of 2 items when I checked everything against my master list when I got home). We didn't think we'd do well on the boardgames as boardgames aren't the focus of the con (maybe I should have taken them over to Manorcon).
Compared to 2 years ago, it was very close; I made slightly more then. Next time I doubt I will bring any boardgames - hopefully I will have got rid of them by then, but RPGs will certainly be returning and possibly books will too. IIRC last time I only took 1 or 2 boxes of books and they didn't do well, but I think the bigger selection helped this time - I noticed there were more sales on Sunday when I got the boxes up on Richard's table after he'd left (plus I think some of the German contingent were clearing out small change).