Ya, people are skeptical about signing unless they really trust you so much. However, if they can't sign, let them write a letter to the Embassy confirming that they will host you in the US and take care of your bills. I know this can work coz my brother had a letter and it was enough. If your personnal account is red, you can get from a friend or family member together with a covering letter saying for example, they will cover your travel costs and visa application process etc.
AOS is good but there are several alternatives which also work eg land title from your parents or any relative/friend, bank statements from any close person to you. Always remember to have a covering letter from that person. You will be good to go.