About copyright

[totala]

Hi, I'm a new artist and I would like to buy some instrumentals from Producers on fiverr as I find them at very good prices. To the best of my knowledge if the seller doesn't mention anything in the gig or if he mention that I own 100% of rights then I own everything based of website contract. In this case do I still need an agreement contract to protect myself? So for example if a seller use samples that are copyrighted to create the instrumental that I will buy and then the owner of samples will sue me, how can I protect myself without a contract made by a lawyer in a court of law? Will only the user contract offered by fiverr protect me? How about giving credit to these producers when I release my songs is it a must or optional? Thank you!