How to check if an exhibition proposal is serious and legitimate?

I have received an exhibition proposal, what should I do?
You have received a proposal for an exhibition or participation in a book, a promotion etc .. The proposal is attractive, here's how to detect that this is a real opportunity:

1. Check on the forum if other people have already dealt with this contact
2. Search public data about this person (on google, yellow pages, forums)
3. Look on Google maps if the address of the place of the exhibition or the company exists
4. Call the person's phone number to talk to them and get an idea

A serious opportunity always includes the following elements:

• The person has a registered company
• The company has an accessible website
• A phone number that can be reached
• The physical address of the place or company address on Google maps
• Often, there are links/reviews available on google that mention this company or its website

If one or more of these elements are missing, beware! A proposal as enticing as it can be can turn into a waste of time and money if your contact is not serious.