AutoEurope does sometimes charge one-way fees and often you don't find out until after you book. That said, they do disclose them in a follow-up email if they apply, so you would know before you get to the rental counter if there was one.

AutoSlash discloses any applicable one-way fees at the time of booking on a pay-later reservation, so you don't have to worry there. You do want to be careful though about prepaid reservations via Rentalcars.com (which are often offered through Priceline). Sometimes they sneak the one-way fees into the terms and conditions and you can get surprised at the counter.

Hope this helps!