Volunteering at and knowing the rescue that you want to adopt from is a great idea. The rescue I ride at, lease at and volunteer at is run by people who are making a lot of sacrifices to save these horses. What frightens me when I see a thread like this one is that so many people are painting all rescues with a negative brush.
I'm sure that there are some out there that are scammers and are out for an easy buck and that breeds the contempt and distrust that I am seeing here, but it also makes it harder for an honest rescue to get donations and volunteers. I'm sure some are dishonest in their descriptions of their horses, but there are many horse 'breeders' that can be less than honest and it is up to the buyer or adopter to do their due diligence.
Volunteer, check out their website, look at their facebook page, ask people who have adopted from them. If they are legitimatly looking for people to adopt and give these horses a loving home, then they will not hesitate to volunteer this information.
The rescue I volunteer at keeps a 'success stories' page going that shows all the horses that have been successfully adopted and most of those folks have come back from another horse or even leave their adopted horse at the ranch to be boarded.
I pay for a full lease, so I am the only one who rides my horse and I pay a trainer for weekly lessons, but I still volunteer my time and energy to the ranch since I know first hand the good work they do.
The hardest thing about volunteering at a rescue is falling in love with the horses you work with and then having to let them go to new homes. While you are happy they are getting a good home and will be loved, it's hard to give them up.