I have an aunt just like that as well... and she is in WDW as we speak.
She was a bartender most of her life at a local restaurant, she is in her late 50's now, but by her mobility, she seems much older.
One night she was at work, and a man came in and had some drinks, and started getting loud and rowdy. She decided to cut him off from having any more to drink for the sake of others around. Well when she left work about an hour later, she was walking to her car, and the man she told couldn't have anymore was so mad because she cut his drinking off, he ran her over with his car and dragged her down the street for approximately a half of a mile. He did major damage to her, breaking both legs, her hips and severely hurting her back. She has had many surgeries and unfortunately the pain is a struggle everyday. She has a bright spirit and a smile that is contagious. And she loves WDW. She can do short distances as well... but not long distances. They just cause too much pain. She is also a person who, judging by the way she walks to and from the bathrooms and whatnot, you would think has no real disabilities aside from the limp she walks with. She doesn't want sympathy or special treatment, she just wants to enjoy life and her family. She hates using an ECV or wheelchair, but knows that if she doesn't, the vacation won't be enjoyable because she will be in too much pain to do so.
I believe that sometimes people are way too quick to judge, and I am not going to lie and say that I haven't looked at someone before and thought "why are they using that ECV, they look fine!". But who are we to know that these people don't have a true disability. I think this is where the subject of having a doctor's note comes in. Because some people are SHALLOW enough to rent an ECV out of pure laziness, and these are the people who make others so quick to judge upon those with true disabilities. I have a friend who has struggles with a thyroid problem all of her life... and I can't even imagine the struggle. I am not an obese person, I was overweight, and lost what I had to lose, and even then it was a struggle and sometimes so aggrivating because I wanted the results so much sooner. And then I look at my friend, who is struggling because of a thyroid problem, and my heart goes out to her because no matter what she can't lose the weight. She has tried everything and I remember the aggrivation I had, nevermind what that girl has to go through. She wouldn't necessarily need to rent an ECV due to her weight, but it would be a long and tiresome day walking the parks.
We just never know what a person's story is, and I think some people take advantage of that, and rent one because they are lazy. And as I said before, these are the people who give the disabled a bad reputation in the park when they rent an ecv, because we just assume they are all ok, because physically we see nothing wrong, and actually we have no idea what really is wrong.
So I guess all I have to say on this topic is, I agree a doctors note should be provided when renting and ECV. I don't agree with renting out just to get around the parks, there are benches everywhere to sit an rest if need be. But I also don't agree with the way that some people are too quick to judge what a person's disability is and assume there is nothing wrong with them.
And now lets just hope I haven't offended anyone lol...