This scam risk would be 1-(.995)(.995)(.995)(.995)(.995)(.995) = 0.97% for 6 prepays in the 3-year period.
The more repayments you a reinvesting lender gets, the greater the risk he will get a scam loan.
The optimal number of repayments for such a lender is 0.
To carry this to its logical conclusion, the optimal strategy is never to lend in the first place.
If you're lending to AA's at 12%/year which compounds, and each borrower holds the loan for a 3-year term, after 18 years you have about a 1% chance of losing your investment (1-(.995)^6).
(For the reinvesting lender who erroneously applauds prepayments every 6 months, it's 1-(.995)^36 = 16.5%)
But over that 18 years (at 12%/year to AA's) you will be doubling your money every 6 years, a total of 3 times.