Note that what the OP reports about the Dollar counter agent and CS phone rep saying that Dollar will remove the FPO charge if you provide a gas receipt is how Hertz now operates its version of FPO:

https://www.hertz.com/rentacar/produ...se_Product.jsp

Dollar may be following suit and behind in updating their web site.

However the actual rental contract the renter is asked to sign is of more importance than what a web site, counter or phone agent says.

And with Dollar, Hertz and any other US major car rental company, the Fuel Purchase Option is an ... Option. One that may be declined and so the counter agent lied on that point.