Hi: I' sorry but I don't work on spec. The concept IS the value of a logo and developing one without at least a contractual obligation is working for free. This kind of arrangement is a disservice to both the client and to the designer and is frowned upon by both major US graphic design associations—GAG & AIGA—as devaluing the industry as a whole. (I can provide you with their specific documents addressing this issue, if you'd like.) You should be able to see from a designer's portfolio whether they have the skills to deliver what you need. BTW, I do offer a 100% money-back satisfaction guarantee. Contact me for complete details.
Mind you, a survey by the Graphic Artists Guild of actual fees charged by established design firms lists corporate logo design at $3000 and up. (AT&T paid over $15000 for their logo and the famous Paul Rand frequently charged $50000 and more for a logo design.)