#1. Where are you seeing Advertisement?
This is really vital,as you’re going to find that mot all of them are from trust places. Usually you have to think about 
this as your first warning sign as to whether or not the company is even legitimate.
#2. Pay attention to how you contact them.
When someone is putting forth an offer by saying something like “we buy houses for cash” you’re not going to want to be calling a random long distance number to talk to them. But rather you want to know thy have a dedicated number because they are so serious about being able to take your call.
#3. Always ask for professional references.
this is a necessity, as it affords you the opprtunity to talk to other companies that have gone through this type of realtor before, usuaslly this comes in the form of other customers, as well as banks and the like that do business with the organization.
Source: Cash Home Buyers Az Blog
Fast Home Selling Tips 