MP, Annie was free
And there's certainly 'nout wrong with her! There are plenty of good reasons someone might need to rehome their horse, and if your circumstances forced you to say goodbye to them even though you loved them to bits, I think a lot of us would rather give them to the right home for free than the wrong home for cash! I have several young friends from Portugal who couldn't take their horses with them when they moved back to the UK and every one of them rehomed their horses for free. Sometimes people just aren't interested in selling.
Annie isn't the first one I've been offered for free, I can think of 4 others I've been offered over the years I've been working with horses. They were all lovely horses and just right for me but I didn't take them because the circumstances at the time weren't right for me to have my own. Although I miss all of those horses I have never regretted saying no as I'm well aware that all sorts of things could have gone wrong had I taken them when the circumstances weren't right. And of course if I'd taken one of those then I would never have got Annie... nor Mouse for that matter as the reason my boss' family got him for me was because I had never had my own. I call it fate.
In answer to the question I'd say don't do it. It's so tempting to have them but I think you have to let your head rule your heart for these things.