We don't have clients that reimburse travel (not that kind of business), but we do #7 too, although it's becoming less relevant the way fares are going. We also allow people to add personal travel at their expense on one or both ends of a trip where permitted by the IRS -- for domestic travel and a few foreign countries.

The tax rules regarding personal time as part of a business trip are tougher for international travel, especially for smallish companies where it's the owners making the decision, and if you aren't careful, you can end up being required to 1099 someone for some of their air fare!

We allow people to take per diem in lieu of itemizing, but it's a pain to use the geographic specific amounts, so we just pick the blanket allowance which is mainly only useful when staying at a friend's house instead of a hotel.

Our basic assumption is that we trust each staff member to be honest until proven otherwise.