what are the advantages/disadvantages of having multiple websites for the same business?

here's the situation. my client has me doing some SEO work on his current website, his MAIN website, and at the same time, he has someone else working on other website and he's even asking me to consider making a 3rd website. i have tried to talk this guy out of multiple websites but i need more concrete reasons to support my argument.

so far, what i can come up with is:

- if there are multiple websites for the same business, then which address do you ask people to visit or publish (in emails, cards, posters, etc)
- secondly, if google should spot both websites are having similar contents, then only one (whichever one google feels is more relevant) will be displayed in search results. the down site to this is that there's almost no guaranty as to which page of which website google will display.

so i need you guys to help me with more reasons why or why not to get multiple websites for the same business.

PS: when i say multiple websites, i dont mean multiple domain names pointing to the same site. i mean completely different websites with different designs altogether.

Main site: www.mountainviewcyprus.com/
sister site: www.mountain-view-hotel.com

you guys should check these pages against alexa and website grader.

kheme: welcome back and happy new year 

I think this is a BAD idea, even if you are paid top dollar to do otherwise.  What he should do is have multiple domains which all link to the same "main" domain.

It is also BAD from a maintenance stand point - When you and/or the others leave and other people need to replace you (it does happen), how do the others know what is going on?

Again, VERY BAD idea. If the guy still has doubts, kindly point him to this post and/or have him contact me directly

lol. if i could point him here, i would have asked him to read the other thousand and one articles i've read. they guy doesnt even have time to send me an email and being that i'm new in the SEO business, he doesnt have much regard for my advices (or at least, that's what i think, lol). i will get the word to him somehow.