I want to get a clearer idea of what travel expenses I can write off, but I don't want to get into a gray area of risky tax practices, so here's my question: If I'm in town for a week, can I treat the first three days as a work trip and the rest as personal time, and write of the airfare and business costs with confidence that I'm not muddying the waters?

If this is a one time shot then fly your friend in but remember housing him costs, transportation daily to work, food costs, airfare etc.

For a few hundred bucks, hotel & air fare... you can immerse yourself in a pool of hundreds of sophisticated and accredited investors.Step #2- Follow up with all the people you met and strengthen the relationship you started. 

And make sure to visit the property-could be well worth the airfare.

The amount of air fare , hotel , rental car, was all a tax write off and well worth it. 

You can also buy a duplex in a place you want to visit so airfare and hotel can be tax deductible against your profits.To answer your question, the IRS deduction on capital gains is only valid for your primary residence not a vacation home.  

Spend your air fare on them instead. 

We're in our 70s now and our biggest expenses are for a new Lexus every couple of years and first class air fare.

Southern European countries can go on topsy-turvy development rides, but despite local rental markets, cheap airfare can help an airbnb rental business work.

Ron offered his tuition partner slot to me in order for me to attend a college at no cost other than my own air fare and we shared the cost of a hotel room.