Anything you do for clients becomes their property. Remember, they’re paying you. If Picasso paints a painting and you buy it, you can burn it, you can trash it, or you can sell it to someone else.
The whole “commercial license” is a bunch of nonsense some sellers offer to get more money from buyers. Fiverr allows it because it also makes Fiverr money.
Besides, how can you write a contract without violating TOS? Contracts demand extremely sensitive information such as names, addresses, telephone numbers, e-mails, tax ID, etc.
If a contract is broken, who do you sue? What if the buyer or seller on Fiverr has a fake account? What if he gives you a fake name?
Look everyone, all you have to do is do your job, deliver, and forget about it. That’s it. Don’t bother with contracts, don’t sign anything, don’t Skype (unless you have a Skype gig), don’t exchange personal information, and you’ll be fine.
Besides, even with a contract, your buyer can do a PayPal chargeback. This is why I fear big projects. Imagine you spent 40 hours recording a 250 page book. How would you feel if they do a chargeback? At least with Audible you’re protected from PayPal chargebacks, on Fiverr, you’re not.