1- If they ask you to pay in order to see if the software will do what you want. That is a sure sign you may become the victim of a smoke and mirrors act.
2- If it takes more than a week to set up a demo that can prove they have the capabilities you need. You might be in for a very expensive solution that after your investment fails to live up to the hype.
3- If the vendor tells you that the value is in the service they offer, and their primary answer to your questions is “We can support that but they can’t show you”. You may be in for some big trouble if you buy.
4- If they can show you exactly what you want to see, and they can do so in a reasonable amount of time, that is a company that you want to work with.
5- If they can provide you with references without having you sign a letter of intent first, that shows they have enough satisfied customers that they have nothing to hide.