How to post a return of a sold asset not in inventory?

Thanks in advance for the help.  This business sells properties to investors. The properties are set up as inventory assets (they do NOT use QBO inventory function or invoicing to record a sale).  A separate system that does not sync with QBO is used to track investor transactions, so when an investor buys a property it is recorded in QBO like this:  a JE to CR "inventory" and DR COGS.  A deposit to the Sales account to record income. The investor has up to ONE YEAR to exchange the property for a different one.  It can take several months before they get a different property.  So my 1st question is what is the best way to record putting the returned property back in inventory and give the investor a credit (a liability owed to the investor) for the full amount paid which will be used to purchase the replacement property?  (remember, they don't invoice to sell a property). My 2nd Q is:  If the investor has a $75K credit and buys a replacement property for $70K but agrees to make it a wash, what is the transaction for the $5K?