I have trouble believing this because saying no to people takes a lot of confidence. If you're disabled, it's more likely that people have spent most of your life telling [i]you[/i] no, saying that there are things [i]you[/i] can't do, and that you're reliant on able-bodied people. In some people, sure, that might breed an incredibly resistant personality, but in most, I feel like it's more likely to lower their self-esteem and deprive them of agency in dealing with other people, especially in such a frustrating job as customer service. Which might making it harder to deny people things rather than easier.