I have a few customers that have varying degrees of disability.
A quadriplegic, and various elderly people with varying degrees of mobility problems.
I recently helped a couple with hearing difficulties (he was partly deaf, but didn’t know anything about computers, and she was totally deaf, but was the main computer user).
It was an interesting experience, but somehow, by speaking clearly (and loudly), I was able to communicate, found their prepaid dialup internet gave a “incorrect password” error, phoned the ISP, and managed to find out there had been a payment error, and gave lots of helpful advice along the way.
All in all, a very satisfying result.