Hi there,
As a self-employed web developer I still tell clients that all my templates start from RocketTheme. There are good reasons for this...
Firstly, it shows that I am being honest with them. Believe me, sooner or later a client will catch you out!
Secondly, they feel more comfortable that should I get knocked down by the big red bus there will be someone that can help them going forward as they can see it is a big community here. 
Thirdly, when I show them some of my sites and then show them the original demo template they often say "Never, can't be the same template!". This just serves to boost their faith that they chose the right developer for the job.
And the last reason, probably the most important reason. Why would I want to pretend I designed a template and steal the glory that rightfully belongs elsewhere e.g. the RocketTheme dev team. I know I get frustrated / angry / furious when someone takes one of my ideas and pretends it is their own.
This post has reminded me of saying I have on my office wall...
If you succeed in cheating or pulling the wool over someone's eyes, don't think that the person is a fool...
...Realise that this person trusted you much more than you deserved!
Regards