If you are searching for information on Google and you find a site that has some pretty good stuff but it looks ugly or unprofessional, do you leave or keep on staying to find other info?
Do you try to find another site with similar info that is more aesthetically appealing or do you just go ahead and deal with it?
It really depends on how "ugly" or "unprofessional" the site looks. If it was bad enough I would bounce immediately.
If it was bad but not wicked awful then I would stay long enough to at least take a taste of whatever written content or other content was on there. The whole time I am sampling that content though, I am going to have a sense of distrust in my mind. That slight sense of distrust will increase and cause me to bounce the first time I come across anything else that rubs me the wrong way on the site.
It's really a call you have to make at that time depending on how bad the site is.
If the reason you are asking is because you want to know "how professional" you really have to make your site, then I would say that "average" is enough to keep most people from bouncing right away. Still, if you upgrade the looks of the site you will help retain more visitors, increase the user experience, increase tendency to share socially and gain a lot of other little combined benefits. For me it is really about whether a site is worth investing money in to have it done somewhat professionally. IF it is a money making site, then probably yes. If the site isn't designed to make money then generally - no.
