2. They ask you to evaluate or review their product..

BIG NO, this is the BIGGEST sign of a false customer. If you are a consultant then they need to pay for your expert opinion. Who has time to do this? This could be a trick for these people to take your advice and leave you in the dust while they use the information that you gave them to do the work themselves.  They may even be smart enough to brag about how much they love what you do first. I call this “Dangling the Carrot.” It’s an effort for you to think you are may get their business if you help them. Don’t fall for it. Tell them you will be glad to evaluate their product once the account is established.