Hi Michelle,
(And Erika) The best answer is that if they are charging money that it is certainly a reason to look hard at them. They may or may not be an actual 'scam', but you really need to be careful.
Some are offering a real service, researching grant sources, writing/reviewing proposals, submitting and negotiation, etc. These are valid services that can be really valuable in saving time, effort, and including information access and resources that you may not have easy access to. You need to research the company carefully. Ask for references, etc.
Others sell lists or 'books' that are little less than copies of internet search results.
Others are outright 'scams' that promise the moon, take your money, and if they respond later at all, it's so sorry, no takers.
Personally, if I am looking for a grant, I'll go to the source myself. One source I've seen that is definitely valuable is the SBA's SBIR (Small Business Innovative Research) programs. You'd be very surprised what they are offering to fund.
Whenever you go looking for a 'grant', the best advice is BUYER BEWARE!
Good Luck!
Source: http://www.abusinessmentor.com