Received an offer for a "wrap around Mortgage" to sell my house for an investor. seems like a great offer. What am I missing?

I need to sell my rental property before the end of this year to avoid capital gain taxes. My renter vacates by September 30th. My plan was to fix it up and list it once he leaves. I reached out to a few local investors and got offers below what I wanted for cash as is purchases. If I can walk away with 70k, I will be happy. I have a 126.5k 15yr, 2 year old mortgage.

I was offered 197k structured as a wrap around mortgage where I receive 70k and then become the lender, keep paying my existing mortgage at 1,270, but am paid monthly by the buyer 13-1400 per month until the property sells, in which case the balance of the loan is paid by the buyer.

This seems like a great deal, I have no work to put in the house. I get my 70k plus a small interest rate on the "loan" I lent to the buyer, plus I would receive an additional windfall after the sale of the house of whatever is paid off from the mortgage payments from my sale date to the buyer's sale date. I understand I will have to get approval from my lender prior to signing. My primary worry is my lender making a call on the balance of the loan I owe once they find out I sold the property. That is my primary concern.

What am I missing here? is this common and safe for me? anyone have any bad experiences with "wrap around mortgages" or "all inclusive deed of trust"?

Some more numbers to clear things up. House as is is worth maybe 210-220k as is, fixed up 230-240k. I have to sell it in 2017 or I pay taxes on income from sale. there are some repairs that would need to be made prior to me listing it of 5-10k, plus the cost of a sale (real estate fee, closing costs etc) My bare minimum is 70k take home. The house rents at 1400, and I am financially stable with zero other debt and plenty in savings, just not much time to fix or manage a house.

Any help is appreciated.