An invention submission company will advertise an information kit or sales brochure for inventors.
The purpose of this material is to sell you their services.
These services are sold like steps on a ladder. They may offer the first step free, which is to evaluate your invention to see if they can sell you their services.
A licensing agent, or agency, does not sell services to develop and commercialize your invention. They may charge you a nominal fee to review your material.
They may suggest what is missing or what you need. Their interest is in making money when they license or sell your invention. You have to convince them that your invention is profitable.
Alternatively, the invention submission company doesn't care if your invention is profitable or not.
An information kit is a promotional brochure explaining the importance of inventors and inventions. It will provide information about their company, their services, and fees. The "kit" usually includes a brief non-disclosure agreement stating that any information you send is confidential. There is also a form requesting a description and/or drawing of your invention.
This is the basic template that an invention submission company sends to inventors.
You should check with a consumer protection agency for any information concerning an invention submission company, including the names of the officers of the company. In the United States, this agency is the Federal Trade Commission. They have a website search.
You can put "invention" in the search field on this site and retrieve information about invention submission companies. You can also use this search field to check the names of individuals or companies.
Ask the invention submission company to disclose, in writing, their success rate for licensing inventions over the past five years. This would include how many clients they have represented and how many received licensing agreements.
Ask them to provide you, in writing, the names of invention submission companies that it or it's officers have been involved with.