"The world is very black and white to him. He thought he was doing the right thing by saying no. But as soon as they're not listening to him, the anxiety will switch on.
"He was very distressed and it impacts on us all," she added. "It takes a while to bring him back to not being angry at himself."
After the Herald made inquiries, the AA apologised to the man and offered him a full refund.
A spokesman, Julian Travaglia, said the salesperson saw that he had previously held an AA membership for four years and was asked if he wanted to take up membership again.
"While he initially declined, when the representative outlined the full range of benefits available to members, he subsequently opted to go through with taking it up.
"Our preliminary investigation has not revealed any undue influence, but we are very keen to talk to [his] family to gain greater understanding of his individual circumstances."
Travaglia said staff were trained in working with vulnerable customers and responding to a range of needs, including people with English as a second language, elderly and those with diverse requirements.
The mother said she and her husband did not want to coddle their son and they aimed to help him become more independent.
They did all they could to make his social interactions run smoothly. They went to the AA branch early on a Saturday to avoid queues and to reduce the possibility of sensory overload. But they did not want to "hold his hand" at all times and allowed him to renew his licence on his own.
"The last thing I expect for him to have to do is go in and explain 'Well, I've got autism' or wear a badge saying 'I've got autism'," she said. "I would expect that in society, if you say no, no means no."
She also questioned whether the organisation was taking advantage of young people by upselling them when they were carrying out licensing requirements, and whether staff were pushed too hard to sell memberships.
Travaglia rejected any suggestion that staff were paid commission or bonuses for selling memberships.
