I highly recommend anyone getting a bill of sale no matter how well you know the sellers. I bought a 1 yr old granddaughter of Two Eye Jack (yes I'm THAT old) years back from someone I had knows since I was a kid...he was a very sweet man. We did not have a bill of sale, because well....I don't know we just never wrote one out and trusted each other. He couldn't find the horses papers off hand so he was going to give them to me as he came across them. Again, full trust in each other.
Well....unfortunately this man had a daughter who was just a mess....drugs/alcohol etc. And...unfortunately the man died. The daughter came across the horses papers, which of course were still in his name. Being that she was awarded all of his property she then considered my horse which was now 5 years old and very well trained, to be HER property. She stole her from her stall and when I called the police she showed them the papers in her dads name and because I had no bill of sale they said I was out of luck. I stupidly tried to take her to court but again, I was out of luck with no paper proof that I had purchased the horse even though I had had it for 4 years.
The horse was sold for drug money and I never saw her again. I found the new owners through AQHA and explained what happend and offered them up 1K over what they bought her for, all I could afford at the time, but they refused to sell her.
Always get a Bill of Sale!