1.) The front desk agent calling their SUPERVISOR is not the same as the General Manager, OP - something others here suggested and I agree about contacting.

2.) Leave a review on TripAdvisor etc complaining about this. The hotel / GM will likely take action because that will scare families away.

3.) Where did you buy the crib? Target? Walmart? Most major stores will take it back, even if opened/used. The reason doesn’t matter.

If you don’t want to keep it and don’t want to go back to this hotel or expend any other effort, just return it.

And, in the future, bring your own - I imagine your own is much, much cleaner than anything any hotel would have that is used by others - especially if you’re driving. As Often1 stated, Marriott does not guarantee such REQUESTS.