There is no one size fits all; some celebrities are happy to just do a voice over, get some cash up front, and go on their merry way.
If you want to continue be able to use the celebrities likeness, lock them in with future promotions or have them take a greater role, then you are going to have to put a little more skin in the game.
Here are the main forms a celebrity endorsement for an infomercial contract takes:
-Front end payment only
-Smaller front end payment with back end percentages
-Partnership where the celebrity actually owns equity in the brand
In some cases the celebrity actually starts or owns the company and product creation, marketing, media buying, and distribution are outsourced, making you a white label vendor or equity sharing partner with them. This does happen, too, so be open to opening up a new white label line of your product in addition to your own. We understand this may not be as appealing to many entrepreneurs so this is usually the last avenue proposed, but it needs to be mentioned.
The big factors for you to keep in mind are:
-Capital, credit, and vendor relationships available, including initial test media buying.
-Potential liability risk for both you and the celebrity for any aspect of the business or the product.
-What you could accomplish on your own on a strict direct marketing basis versus what the celebrity would add.
Consider all the financial and other ramifications before you make your deal. The other big factor of course is the celebrity, their current level of fame in their career, and how they prefer to work.
Catch the right celebrity at the right time like Salton did with George Foreman and it is a rocket ride, but not all deals work out as well. George was able to devote himself pretty much full time for a year and a half to make the grill a success, other celebrities may not be able to do that.