No, you can sell your car with one key. But a dealer will notice the missing spare when they appraise it, and it can come up when they confirm the offer. So find every key you have before you ask for offers, and be upfront if one is gone.
Why a dealer asks about keys
The next owner will want a spare, so the buyer has to think about what it takes to get one made. Newer cars often use fobs or chipped keys that have to be programmed to the car. That's why "how many keys?" is a normal appraisal question, not a trick.
What to gather before you get offers
Every key and fob. Check drawers, other cars and old bags.
The valet key or key card, if your car came with one.
Say so when you describe the car. Offers are confirmed after a physical appraisal, so the dealer will find out anyway. Telling them up front keeps the first number closer to the final one.
Ask how it changes the number. When you have more than one offer, you can see how each dealer handles it.
Don't rush to buy a spare. Get the offers first. Then you can decide whether a new key is worth it.
Let dealers compete for your car
With PriceForMyTrade, you send your vehicle details in about 30 seconds. Participating local dealerships contact you directly, and first responses typically come the same day (not guaranteed). It's free to you, and you don't have to buy another car to sell. See how competing offers work, or read about selling your car in East Texas.