Disadvantages of acceptin to take 2nd position mortgage as seller

[Blake Hynes]

I have an offer from a buyer to buy my commercial mixed use property I paid $330k for a year ago which I put down 25% on and owe about $240k on.   The buyer is offering $410k which is probably right at what it would appraise for and what I am asking. The offer is also contingent on my holding a $80k 2nd position mortgage at 5%.  I havent asked many questions yet but my biggest concern is that it is the entire down payment. Most banks require at lease 10-15% down in cash from the buyer unless this buyer has a bunch of collateral.   My biggest question is what are the biggest downfalls for me?  I understand the risk of the person not paying me back.  Do I have to pay capital gains on the full profit from the seller or is the portion paid back taxed as an installment sale.  Is there anything else I should be weary about by taking the 2nd position?