Standard "mileage charges" in the US are actually set by the IRS. I assume it's similar in other places so that's a well-established practice for car-related expenses. I'm not sure how else you would do it as there's no way to directly capture expenses other than fuel.
I assume that in most cases billing some standard travel day rate/per diem (perhaps based on location) would be fine as well with, possibly, air charged separately for the actual amount.
The key is that you're being explicit that you're not charging the actual amount but rather some standard rate that, in principle, approximates average/typical expenses.
There are similar mileage rates in the UK, published by HMRC. They have the same purpose.
The mileage rate you agree with your client needn't be related to those rates at all.
I was just asking. You are putting "travel expenses" @ $xxx which doesn't seem to include your rate; so it should be how much you spent to "get there". If you want to charge extra (and I think you should since it's time you spent for the client) then maybe put "travel expenses" + "x hours spent traveling".
In the UK there's, for example, a standard "mileage charge" which people tend to claim for driving to a place for work. It's not "the cost of travel" it's an approximate.
When a company charges for sending an operative to a site, they pay the operative £10 ph, and charge the company receiving them £100 -- presumably you think that's fraud too?
How about when Guchi (made up company) charge you $500 for a plain white tshirt made by people who aren't paid a living wage, wouldn't that also be fraud under the same sort of consideration?