99Designs has a money-back guarantee if you don't like any of the logos. Not sure how good they are about actually honoring it. You get a lot of crap and super-generic logos, but (in my experience at least), there are a few good ones
The base option includes a money-back guarantee but you quickly learn that keeping the not guaranteeing a winner for your project will keep good designers away.
I've worked with 99designs a few times and liked the outcome but potential customers should be aware that keeping the money-back option on your project and sticking with the base price will get you generic looking logos.
If you want to attract quality designers to your project, you'll need to increase the amount you're awarding and guarantee the payment (opt-out of the money-back guarantee).
Again, I liked working with 99designs but you'll have a hard time finding something unique and amazing at the $299 price with the money-back guarantee option. I'd recommend working with them but set your expectations accordingly.
I've used 99D on behalf of about a dozen clients and the cheapest we've ever gotten a great logo for was about $1300.
I'm sure some people have been happy with the lowest price point, but every time a client wanted the money back guarantee they ended up using. Every time I convinced them to opt out and spend a little more they were generally happy.
I paid about the same and was happy with the results.
One more note for people considering 99designs. You can increase your award even after you start the project. Meaning, you can try out the Bronze level design for $299 and hope to get lucky but then raise your prices when you see the generic designs flow in.
When I say generic designs, I mean the designer will take what is essentially clip art and change some curves, colors, and lines to give you a "custom" logo.
Again, that might be good for what you're looking for but at least now you have your expectations set properly.
