Gabriel,
1.) How do you approach a seller about subject-to financing?
Answer:
Subject to is not about the approach as it is a technique. If you determine that this is a deal, the easiest way to "approach the seller" is to show them actually what it will cost to sell their home. Use the current market. Don't get in all the DUE ON SALE stuff when explaining it to them. Just show them that you can buy their home this way and relieve them of the debt for making the monthly payments.
2.) How often do lenders call the loans if it has a "due on sale" provision? Has anyone here ever had that happen in a subject-to deal?
Answer: Super rare doe they call the loan due. I have only met a couple people that it has happen to and one of them had it happen to them because he did not up hold his end of the deal. Meaning that he did not make payments. They asked for the money that he did not have. Seller did not have it and the home went into foreclosure and the seller got axed.
Doing a sub2 deal is like going on a 1st date. It is time to wine and dine them. You never opened the door to your 1st date and ask for a kiss.