I've used Holiday Autos for a voucher to rent a car for a week from the Sixt company in Rovinj. I'm just wondering if I should contact Sixt and make sure they have a reservation for me, or if I can feel confident that they will accept my voucher when I get there. I've not rented in Europe before, but everything looks okay in the paperwork - dates, times, addresses, etc.. But like most companies, Holiday Autos has some great and some not so great reviews. The rental fee just seems a bit low; I just want to make sure we don't get there and they're clueless.
They are probably legit. Holiday Autos is just a broker like Auto Europe, Kemwel, EconomyCarRentals, etc. They negotiate very cheap rates. Sixt is a legit company (I've rented from them in Slovenia and Croatia before - big multi-national company like Hertz etc. just not quite as big). Don't remember where the rental office in Rovinj might be - I remember where the Oryx rental office was, because I walked by it every morning on the walk into town (even though I rented my car from a different Oryx office). Just figure out where the Sixt office is on a Google map.
Wouldn't hurt to contact Sixt to confirm the reservation ahead of time, but they've probably got it.
The thing you have to think about is the CDW (Collision Damage Waver) insurance. Sixt will surely try to upsell you on that. Just figure out ahead of time how you want to handle it, so you won't feel pressured when you are picking up the car. All rentals include liability insurance. CDW covers damage to the car. Holiday Autos might have offered you CDW insurance too. Usually there's an "excess" included (like a deductible) and you can pay more to lower that, even to 0. Some people use their credit card's auto insurance coverage feature for that. (I got burned by that once - in Croatia but not with Sixt.) Anyway, just figure out ahead of time what you want to do about the insurance. Look on Sixt's website to see what they might charge for it. Then when you are picking up the rental, you have no questions about it.
I suggest bringing a smart phone for GPS as well - no need to pay extra for a GPS.
And if you plan to drive into Slovenia, you'll need to buy a vignette driving sticker at the border or risk a big fine if you drive on Slovenian highways, FYI. Croatia uses tolls instead on their highways.
Finally, you may need to get an International Driving Permit (IDP) to drive in Europe. Croatia MAY not require one anymore. But other countries (Slovenia) might. In the US, an IDP costs about $20 at AAA and is good for a year; you can usually just walk in and get one on the spot at AAA. Fill out the application ahead of time to save time from AAA's website, and bring passport pics too or they will take them there.
I always book my car hire through Holiday Autos and have done for years for several trips a year. I have never had any issues when arriving at the desk of whichever operator I am using and I don’t check they have my reservation in advance.
Holiday Autos is just a consolidator, they don’t directly hire cars. I never pick the cheapest operator and I check the reviews of the particular companies.