Hi...we wish you luck in your venture into the world of renting
DVC reservations!
First--all financial considerations are totally between you and the owner from whom you rent...I've never heard of an owner tacking on fees (there is no tax on DVC reservations), but I suppose they could...one possiblity that comes to mind is that some owners use PayPal, which has a transaction fee, and some of these owners charge the renter an additional amount to cover that fee...others build in that fee in their price per point to rent.
Also, the owner has to add the dining plan and Magical Express--if you the renter want either or both of these programs--ME is free, but the
DDP the is paid for at check-in. The renter pays Disney directly for the cost of the dining plan.
The reservation is made in the renter's name, and no the renter need not "pretend" to be an owner. Renting is perfectly legal and you can "admit" to being a renter--altho in my experience, the issue has never arisen. I'm an owner, but have been asked for my owner's m'ship card only when using a member-only perk (renting does not entitle you to use member perks)... the CMs at check-in simply do not ask if you're an owner or a renter, and it has never (in my experience) come up...I have taken guests, who stayed in separate villas, and they've never been asked if they're owners or guests (or renters) either...but there's not a problem w/admitting to being a guest or a renter should the question arise for whatever reason...
I guess one possibility that comes to mind are damage charges/fines...e.g., there's a fine for smoking in a non-smoking area (don't know the degree to which it's enforced), and owners are responsible for damages done to villas, whether it's the owner staying there/doing the damage, or their guests/renters...if you find yourself charged a fine because someone smoked in your villa, or if you cause damage to the property, then the fact that you're renting could well come up...I'm sure the owner will hold you responsible for either of these charges, but Disney will hold the owner responsible...so that is an issue you'll find discussed by the owner when you're discussing rental terms...
Bottom line to renting: Disney allows us owners to rent our points (so long as we don't make our rentals into a "commercial enterprise"), but stays completely out of the transactions. So all details of your rental agreement will be between you and the owner from whom you rent. Disney won't get involved if you have a problem, nor will they allow you to do any "owner-only" tasks yourself (the biggest one of which is making/confirming reservations--only your owner can do that; you cannot)...
Good luck. The vast majority of rentals seem to go smoothly and result in happy renters and happy owners--but do use some caution and do understand that you're dealing w/an individual, not a corporation...the individual stands to lose points if you back out of your rental agreement, and the the "pain-in-the-tail" factor of renting is such that some owners are simply unwilling to accommodate cancellations...just make sure you discuss all these details with your owner and get a feeling of trust and good will between you and you should be fine...
Pixie dust to you...