It is certainly NOT only US companies that have some extra minor fees, they do in France for sure (the only place I've rented).

I think Autoeurope is a fine company, I've used them before, but the glowing review turned out to be based on no problems having occurred. So take that for what it's worth.

In fact, the thing that I dislike about Autoeurope is they claim they will match any rate but they will NOT match discounted rates you get for special memberships. For example, I get a cheaper rate through Hertz in France just using my US AAA membership than Autoeurope will give me, considerably cheaper. And don't say all I had to do was ask AE, because I did and they said they will not match any discounted rate like that.

If you book thru AE US site for France for example, it shows that there are charges in addition to your prepaid rental which can only be paid locally, but if you book thru another site eg AE UK site, there are no additionals to be paid locally, it can all be prepaid except for things like optional extras like additional driver charges, GPS, child seat etc. Everyone books thru a different storefront (UK, US, FR etc depending on where you live) and the rules are different according to what can be prepaid and what must be paid locally depending on which site you booked on, it's not one size fits all. The extras should not be a surprise if you've read the Additional Info/Local Charges information.

One tip that I can give for one way rentals, whether through AutoEurope or directly through the actual company, is that if you rent out of a small agency, you are highly likely to be automatically upgraded. This would be a total mystery to me if I had not worked at Avis for a year in olden times. There is a system for company-owned agencies and privately-owned agencies for dealing with who owns which car. Back when I was working for Avis, the basic deal was that whoever has the car can rent it for two weeks and get the revenue, but after two weeks it has to be sent back to the owner because the revenue sharing changes and if the wrong place has the car, they end up getting nothing for the rental. So it is very important to send cars that you don't own back to the owner, or at least in the right direction. The good thing about returning to Paris is that all of the rental companies have major company-owned agencies there, so it is the perfect solution for other agencies anywhere else in France to give you whatever car they need to get rid of, the bigger the better. I always reserve the cheapest category A car, but I have been given BMWs, Mercedes, Alfas and other such cars from cities like Mulhouse, Metz, Valenciennes or other "minor" cities that need to get rid of cars that don't belong to them. It's a gamble, but hey, I am happy with driving a Fiat 500 anyway.

On some roads a smaller size is preferable.

Absolutely. That is why I only appreciate these upgrades when I am returning to Paris.