Regarding discrimination, I think the original poster may have a point. While I don’t think there is direct discrimination (i.e. dealers aren’t saying “we won’t deal with you because you are disabled”), there could be indirect discrimination. Does the policy of prioritising retail customers put disabled people at a particular disadvantage? I think it might do.
If it does, then dealers need to show that the policy is a proportionate means of achieving a legitimate aim. I don’t know the industry well enough to know whether dealers can show that. But I think the issues would have to be explored before eliminating discrimination.