I have an iPhone with issues, MEID and jailbroken

I would like to start with "I know nothing".

My iPhone was purchased directly from the Apple store, I've never tried to jailbreak or unlock it, so I don't know much. I'm trying to help a buddy out and sell this phone for him, but its getting complicted.

A friend of mine was given an iPhone 4S from a friend, who said it was jailbroken and with a clean ESN.

My friend needs a little cash so I'm going to sell it for him, but I don't want to sell something I'm not 100% about, and I'm so curious about all of its little issues

It is a

Verizon iPhone 4S 16GB

They both swear it is jailbroken. With all of the googling I have done, I cannot find a way to confirm that it is jailbroken.

There are no weird apps, none of the factory installed apps are deleted, etc.

Is there a foolproof way to determine whether or not it is jailbroken?

Also

I called Verizon with the MEID to see if it was clean or not, and she said "device not found"

An MEID is supposed to start with a letter (A-F)

The MEID on this iPhone starts with "990..."

It is the same as the IMEI with the exception of the last number

What is going on with this phone?

Thanks 🙂