Well I suppose if you need the work, and they need a site, and they’re cool with a themeforest theme, I say go for it. They would have to know it’s a themeforest theme though. You can’t not tell them that.
It’s not about $5k website designs or whichever metaphor people would like to use. A simple site can be fairly inexpensive and custom. Using themes only shows lack of creativity and the ability to work in this field. Not a fan.