Can you get references?
This can be a tough one. References are a great source of recommendation as to whether you wish to do business with a new vendor. Sometimes, you might end up with a great deal simply because the company has few or no references. In such cases, you are the prize possession of that vendor and they will bend over backwards so that you become a valuable reference.
On the other hand, companies that make up excuses for not having references should not be dealt with. Several common examples of refusal to provide references are (a) We are under NDA (non-disclosure agreements) and cannot reveal our clients, (b) We're in beta (c) We honor our client's privacy and do not release that information.
If a company has been around for very long, they have references. But when they refuse to put any out, it's more likely that the references aren't good ones.
Also be sure to ask for references from former clients. Current clients may give great references because their business dealings have been limited or very recent. It's also easy to cherry-pick your current customers to give great references.
Any company that has been around awhile has former clients, simply because the customer has no need for the service anymore. These will still gladly give good references. If the company cannot come up with former clients with good references, there might be a good reason for it.