When you are shopping for a stairlift ask the sales rep if they have knowledge of their products. Sales reps should have extensive knowledge of the stairlifts they sell. They should be able to point you in the direction of the stairlift that will best fit your staircase.
Ask for information on the company. Ask how long they have been in business, if they have insurance and whether or not they have testimonials from happy customers. You should also ask about installation and service. Find out about the warranty length and inclusiveness.
Investigate the company you are considering purchasing your stairlift from. Find out if they have had any negative press. If the stairlift you are buying is used ask how old it is. Find out is you can get parts for the unit should something break. If your staircase is curved finding one secondhand is unlikely.