What is an ESA Letter and How does it work?

I just want everyone to understand the struggles someone with a service animal faces. I hear of so many horror stories where service dogs are bitten several times to the point of they are reactive to other animals. It can literally ruin a sweet and beautiful dog. I am half blind but luckily can see some things. What if I was completely blind and did not see this untrained animal coming to take my dog off of his job? I used to be all for bringing your "Pets" into the hardware stores but it has ca