Seller financing with 10 year lock-in period

[Brian Toberts]

I am about to close on my first investment property deal, two triplexes in Oregon.  I have a relationship with the seller and we are negotiating the terms with seller financing: 30% down, a 30 year mortgage, at 5% interest with a 10 year balloon payment on the remaining balance which can be extended if both parties agree.  The seller would also like to add a "lock-in" period (no refi or sale) of 10 years.  This term seems very long.  Is it common to add lock-in periods and are there traditional lengths?  Are there any out clauses that I can add?  I am fearful that life happens or an opportunity might come up in the next 10 years where I might need to sell or take money out.  Any comments or suggestions would be appreciated.