Walking into a rental car dealer should be a simple task. Walk in with a reservation, your ID, and your credit card, and walk out with a set of keys. But more often than not, picking up and returning a rental car is a dizzying array of add-on offers and potential fees. How do you make the most of your vacation without getting tripped up by unnecessary costs? Condé Nast Traveler has some smart tips for keeping it under budget, and we’ve added a few tips of our own as well. Because you can never save too much money.

1. DON'T BUY EXTRA INSURANCE.

Are you paying for your rental with a credit card? Your credit card company likely provides its own rental car insurance. Your own car insurance, too, will often cover rental car trips. Check with both to determine whether you really want to spend extra on the rental company’s collision damage package. No, you don’t want to be fully liable if you total your shiny rental car. But that doesn’t mean you need to shell out a pricey daily fee for peace of mind. In fact, some credit cards don’t offer rental car insurance if you’re also covered under the rental agency’s collision damage waiver, so you may be shooting yourself in the foot if you get it. Make sure to check whether your credit card coverage is primary or secondary insurance, though.

2. DON'T BUY THEIR GAS.

At some rental car agencies, you can prepay to have them fill your tank after you drop the car off. That means you’ll save time on the way back, and generally, the price-per-gallon seems relatively cheap. The problem? You’re probably not going to run your rental car down to empty right as you pull into the return lot, and then you’ve just given the agency free gas. It’s never a good idea to leave filling up to the agency. Unfortunately, that’s doubly true on the return end if you've opted for the prepay—you’ll get hit with a huge premium if you forget to fill the tank and have to buy gas from the company when you’re handing over the keys. You don’t want to get stuck paying $15 per gallon.

3. AVOID THE AIRPORT.

It’s super convenient to hop off the plane and go right to the rental car agency, but that convenience comes at a price. Airports charge rental agencies concession fees to operate on their property, and those costs get passed along to you. If you can take a quick (and cheap) train or cab ride to a nearby agency a few miles away from the airport, you’ll probably pay lower rates.

4. FIND A DISCOUNT.

If you’ve got a travel credit card, you might get a discount at some rental car partners. Citi cardholders, for instance, get up to 20 percent off Hertz rentals, while Visa cardholders can get up to 25 percent off National car rentals. Chase’s Sapphire Reserve credit card gives discounts at Avis, National, and Silvercar.

Your employer may also provide rental car discounts, as do some airline and hotel rewards programs. You can even find a discount on Groupon. So don’t reserve blindly. A little research into coupons could save you significant money.

5. DON'T BOTHER TO RETURN EARLY.

In most cases, it’s better to show up early than late. But with rental cars, you can be penalized for returning your car too early. Depending on when you return it, you could be charged a different rate than what you originally planned. If you return a car on Saturday morning instead of Sunday morning, you might end up with a weekday rate charge instead of a weekend rate. If you have a weekly rental, you’ll be paying for a full week whether you return it after five days or the full week. If you return a weekly rental after four days, you might end up paying the day rate, which could be more expensive. In short: You want to stick to your original plans as much as possible, and if you do need to return your car early, call the agency first to check how it will affect your bill.

[h/t Condé Nast Traveler]