Personally I find this debatable, you have the upper hand of it being written in ToS… But I think it’s open for interpretation, it’s almost impossible for web designers (digital marketers and some graphic designers) to sell their gigs, if they don’t show their samples.
It’s a norm to take a look at their previous work before hiring. The ToS is designed to be broad, but I believe it can be debated… It will be nice to hear what web developers think of this.
Personally I’d stressed to potential clients that I only work on fiverr, before giving them my Gmail, just so I can evaluate their ad campaigns. It’s almost impossible to skip this step (at least to me) to evaluate how we can help the client.