[trebleshot]

A price guide is nice in theory, but the market for toys fluctuates so much that any price guide is almost always out of date before it's even published. Of course, the older a toy is, the more stable its aftermarket value becomes.

ToyFare used to have a very robust price guide section in its early days, but ended up reducing it to specific lines that were highlighted each month. Sadly, the whole magazine is now out of print.

The only one I know of offhand that is still in publication is Lee's Toy Review, but their guide's coverage is kind of limited, unless you're a Hot Wheels collector.

Also, even with a price guide to give you an estimate, it doesn't mean anyone else will be bound by that price.

The best advice I can give is to ask fellow collectors about the value of a toy. They may even be able to work a deal with you outside of Ebay for a lot cheaper.