Actually, I see this quite often at shops all over. One posted the full name and amount of unpaid bills on their very large outdoor sign. Others post pictures of bounced checks. If the mechanic is the shop owner, he can do what he wants with his property.

And as far as I'm concerned, this applies to the web, too. If the web designer still owns the domain and server, go ahead and deface it to their hearts' content. If the client owns that stuff, however, the unpaid designer should just take back their work and let the client deal with the blank website.

At the tiny webshop/webhost I used to work at, we would just switch to a plain white page with a header saying "please contact accounts@host". Embarrassing enough to push for payment, but visitors needn't necessarily assume foul play.

Enabling people to save face is important - I doubt these fitness guys are going to be particularly cooperative after being shamed.

If you don't pay the mechanic, you don't get your car. If you don't pay the webmaster, you don't get your website.