You, as a non-owner, don't actually "rent points." You rent a reservation from a
DVC Member, that member makes a reservation for you, so if one member only has enough points for 2 nights, you can rent that reservation and find another member to rent you a reservation for the remaining nights. But it would certainly be more convenient to rent from a single member. My suggestion for novice renters would be to use a service, like David's, the sponsor of our Rent/Trade board. It costs a bit more, but that way you can try out a rental experience.
Also, almost all owners consider the transaction "final" no refunds...but some maybe willing to work with you on changing dates...that would depend on the individual owner and working within their use year for their points.
DVC nor Disney will step in if a deal goes sour, it is like renting a vacation home from a private individual...you are NOT renting from Disney, but you are afforded the onsite perks like any other onsite guest. You also will not receive daily housekeeping, only trash and towel service on day 4 (of a 7 night reservation) or full housekeeping on day 4 (of an 8 night or longer reservation). Additional housekeeping is available at an additional charge.
Most owners want 50% up front, many want the balance paid in full upon receipt of confirmation. Some owners will give you time to pay the balance, if the reservation is several months away AND if canceling would allow them to bank any points , which depends upon their use year. But all payment arrangements are between you and the owner.
Always do business with a person only if you are comfortable with them. We do have fairly strict posting rules for our Rent/Trade board, but there has been the occasional scammer. Look at their posting history, talk to them on the phone, and get an overall "gut feeling" about the person to whom you are going to send $$. Remember than renting is primarily a matter of trust for both parties. Owners trust that the renter will not trash the rooms, leave a charge balance and will pay for the rental according to their agreement. The renter trusts the owner to not cancel the reservation. The DVC Owner ALWAYS has control of the reservation.