Hi Ryan, hope you are well.. I've never actually done one of these, but have had a couple of people, who were not current tenants, inquire about my willingness to do it. Bottom line: I am not willing to do it unless I've already had them renting from me for at least one year and know who I am dealing with.
Now that I've got a long history, I would be willing to do this, but only if the tenants were VERY good and demonstrated a desire to stay long-term and follow-through on all aspects of the agreement. Basically, this would switch them from being a tenant to a potential owner - and change my role from landlord to short-term financier.
Like you, I've heard various ways of doing his. But, I would insist on a 5% down payment, a $200 per month rent premium that would go towards their equity, a fixed time to pull trigger and they get their own financing and also that they are now responsible for all repairs up to a set limit.