Also, my lender now won't refi one of my rentals without a score above xxx because I own too many properties. 

At the highest level of detail, the bid should have a detailed breakdown with the prices for each room, "Kitchen Cabinets, $XXXX; Kitchen Tile Floor, $XXX; Kitchen Drywall, $XXX; Kitchen Plumbing, $XXX". 

New rent rate will begin on XX/01/20XX, and will be $XXX."

I have a unit that may be a better fit that rents for $XXX more.

for example, as opposed to starting my own lending company and getting all the required licenses, I could just make an agreement with a lending company and say I have xxx amount of money that you're welcome to use for xxx amount of real estate financing loans, provided I get an X'% guaranteed return. private person ----> lender-----> lendeeI want to know if this is a common practice?

If a short sale is presented as "bank approved price of $XXX,XXX", you can still offer less but the bank has said that number is one they'll accept. 

Tell her the $900 rent was only a stop gap until she moved out on XXX day. 

Perhaps try testing the market:  run an ad in your favorite media saying "beautiful apartment, $xxx/mo, available (after date of closing)". 

The new rental rate is $XXX more than the one you are living in and we would be glad to break your lease, at no penalty, if you apply and are accepted."

If a lender says "I can get you $xxx,xxxx, with x points at x% interest" without having looked at the actual deal you're working on, they're probably just blowing smoke.