The handicapped seat problem is interesting. One of my good friends is in a wheelchair, he is 28 and has been in one since birth. He drives with hand controls. He usually doesn't park in handicapped parking spots unless the lot is full and there isn't enough room for him to get out of his truck with his chair in a normal spot.
He has had some unique experiences for sure. One time he parked in a handicapped spot but had not gotten out of his truck yet when he was around 20. This lady in her 50s came over and starts yelling at him not to park there. She shut up once he started putting his chair together. Some people are just assholes but most people will hold the door for him or move stuff in store aisles so he can get by. He had one guy in his 40s ask him if he was in vietnam.
It seems most people will keep to themselves or be helpful, with a few that are assholes or make strange comments.