Hellobee Boards

I don't know how a base is affected in a collision, presumably it'll suffer some damage and may not be as safe. But on the topic of buying car seat/base pre-owned, I think it all depends on the situation, where you're buying from, the condition of the item and how much money you're paying. We've bought a used car seat in excellent condition from a very nice family in a well to do area for very little money and not had any problems with it. I wouldn't buy without going to see the item and the sellers though.

We bought a used base.

No, same rules as carseat buying. From a trusted family member or friend, sure, but not of unknown origin. Also, compared to the bucket portion, the base remains in the car & is exposed to extreme temp fluctuations which deteriorate the plastic more quickly. You can often find bases on sale for really cheap.

If it's not expired, I would buy a used one (from reliable source).

If it is expired, the base is still plastic, and still has the possibility of having plastic that is too old and won't keep the car seat where it's supposed to be in case of an accident (cracking, etc).