A bonafide sale clause is a contract restriction that forces you to stay with lender until the term is up, unless you sell the property non-arms length.  Even then, the penalty when you break the mortgage early if you sell can be much higher than standard mortgage products!

If you try to refinance, go to another lender, or seek lower rates in a more competitive market; the lender will sue you for breach of contract!  Avoid bona-fide sale clause mortgage products, even if their interest rate looks shiny and low, it could cost you thousands more in the long term.