They would certainly not sell it for $215K. Its not worth that. They might indeed sell it at $95K, or even a bigger discount. Under some circumstances, they might be able to sell it for a premium.
Bonds are just loans, and the math works the same for both.
In your example, the face value of the note is $100K and its yield is 6%. If a buyer wanted a 6% yield, they would pay face value. They would receive the stream of payments totaling $215K over 30 years, which is the 6% yield.
If the buyer wanted, say, 8% yeild, they would need to buy at a discount. The payments ($599.55) and term (30 years) are fixed. This buyer wants a higher yeild, 8%, so the value is lower. That's a PV (present value) calculation, using the payment, term, and the desired yeild. That gives a value of $81,708.
Now, maybe a different buyer only wants a yield of 4%. Repeat that calculation with a yeild of 4% and you get $125,582.
Bonds work exactly like this. They have a face value and a fixed interest rate. They trade based on today's interest rate. So, if today's rate is lower than the rate on the bond, you have to pay a premium to get the higher yeild. If today's rate is lower, you buy at a discount.
In your example, the guy who was selling his owner carry note would certainly sell at a discount. 7% is just over current rates. A buyer might want, say, a 10% yield. So, they would pay a pretty steep discount. If the seller managed to make his note at, say, 12%, then he might come closer to face value, or even a bit of a premium if it was a seasoned note with a good borrower.