Seller financing question

[Steven Trumpet]

My friends Dad is selling a commercial property & while we both invest in real estate we're unsure of the process & what a fair interest rate should be. 

The last time I read up on this, I remembered the importance of having the lien recorded etc. So far, my friends Dad & the buyers have attorneys and they're offering 4.5% with 10% down. Can you let me know if this sounds fair & what other guidance you can offer?

Thanks in advance!!

Steven