BobKamman
Level 15

Substance over form, and we can only guess whether he drove a thousand miles delivering pizzas, or 10,000 miles selling expensive jewelry.  I wouldn't create paperwork to show a lease that doesn't exist, at least at arm's length.  I would call the use of the vehicle a gift from the parents, and allow him the deduction.  See the Tax Court opinion in Lang, 

 https://www.ustaxcourt.gov/USTCInOP/OpinionViewer.aspx?ID=9397 

-- which involved a mother paying medical expenses and property taxes for her adult daughter.  An IRS auditor with nothing better to do might challenge use of SMR as the best way to value the gift; so use actual expenses, or at least keep a record of them.