Yes, I just give them links to other websites I’ve created not the source files. That way they cannot use my samples as theirs. But still, even some ask you to send them custom offers and then you don’t hear from them ever.
But I’ve once been in the situation you mention. One buyer told me to create a landing page as a test for the work and send it to them so they can tell me if I’m good enough to work on their task.
I quickly came up with something amazing and send it to the buyer, some few hour later this is what I got, “The hiring manager liked your work but she preferred to work with someone whose time zone and hers are a bit closer. We will be hiring again in the next few weeks.” And just like that, I’ve never heard from that buyer ever again.
That happened when I was still a total newbie on Fiverr. I wanted to make my first sale so bad that I ended up being scammed and doing free work.