I've been doing travel recently for the company and have learned a TON about both how much and how little they care about the expense report.
Drove to Texarkana from Louisville awhile back in my personal vehicle. Charged the company mileage, but used the company card to buy gas. Sounds like double dipping except our expense reports have a specific column for that. So it take my mileage, multiplies by rate (currently (0.585), then subtracts fuel from that and credits me the remainder. Boss didn't know this existed and we ended up in about 3 meetings, culminating with the CFO to review the process and make sure everyone was on the same page. Nobody was upset at any level, just turned out about 1/2 the company didn't realize it worked this way despite being very specific in the documentation on how to fill out expense reports (which apparantly was written about 5 years after anyone in that group had started)
Next 3 trips I thought I would be smart and fly down. Bought upgraded seats so I could have easy change of time/date to depart. When I did have to change the flight, all kinds of odd returns came back on the card, then were charged again. yet another 3-4 meetings for them to figure out why I had 12 transactions (some credits, some debits) for a single trips worth of plane tickets. To make those matters worse American wasn't great about getting me reciepts for most of that, so I was printing confirmation emails with time stamps. It was a mess.
The best one yet though was my rental of a storage unit in Texarkana without asking the boss first. Was down there on a Friday, and before I could leave I got a call from the customer "How soon can you be back". Well I had two pelicans of tools with me that I was going to check through as baggage. Instead of paying for the checked bag fees to get them home, and then back to TXK, adn then home again. I just went down the street from the hotel and rented a 8x10 storage unit for a month. Cost $45 for the unit, and $12 for a lock. Saved the company probably $500 or more in bag fees. Once I explained the situation and the reasoning I got a pat on the back, but leading up to that there were some serious tense moments with one of the accountants making statements about defrauding the company and such.
It's fun times for certain!