I am a Principal in an organization in which sales, sales management, and sales promotion account for the functionality of the entire organization. I have found sales promotions to be the most measurable when the goal is to promote repeat business or loyalty, rather than prospective business. Depending upon the kind of incentive aimed at new prospects, all to often the individual just takes advantage of the promotion and that is the extent of business. Whoever you go with, I urge you to stress repeat business from your customers. Not only do they like taking the promotion and their perception of your appreciation for their business is an intangible that you can not put a price on.
Regards,
Charles