So i am fairly new and i don't want to get low balled by someone who's been doing this for longer than me. What do i do if a trader claims that the package has not been delivered and the tracking confirms that it was?

First, if you're referring to this trade, start a BTR. That person has had multiple BTRs filed against him for bad trade practices.

Otherwise:
Did you tell them that you got tracking? If you didn't, tell them and give them the number and see what they say then. If you did, double-check the receipt/paypal email to make sure the address was correct. If the address matches what they gave you and they still claim to not have received it then it would probably be up to the admins to decide what to do. I remember seeing a BTR for a similar situation, but I don't remember the outcome.

Hope this helps!

Thanks for your help, but I'm not sure how to start a BTR

No worries. Go here and post a new topic following the structure found here.