That's actually a pretty good reason.
So there's 2 things. Webmaster tools and analytics.
First, regarding webmaster tools.
You can't easily fool webmaster tools because its all internal at Google (best you could do is mass fake the statistics that generate those internals). For instance, if a certain website exists for which you want to generate fake activity for it ... lets say its average searches 800 per month, and you're in the top 20 (which means maybe 200 people would see that link). You could brute-force a ton of searches from various IPs, have them view the 2nd page, and this would influence webmaster tools to show the increased impressions. You could take it a step further by having those bots actually click your link, and it would influence webmaster tools to show the clicks as well. This requires a bot that scrapes and interacts with Google.
Second, analytics.
Google has no idea who visits your website, this isn't an internal functionality with Google. Thats why you got to put analytics code on your pages, so that Google gets told who is visiting your website. If you want to fake Google analytics, all you need to do is fake traffic to the analytics code.
Now, most of the traffic that Google sends a page nowadays is anonymous ... like 90% of it. 10% actually shows the keywords, because searches are being performed in unencrypted mode (the person isn't logged in to Google, etc.) If you're getting like 10% anonymous and 90% showing keywords, that at face value is fake.
You could automate a bot, where you have access to a number of proxies. Now whether you're using PHP cURL, or directly using internet explorer (through VB6 or VB2012 which I'm accustomed to) and certainly through any other scraping software ... you've got access to headers. Referrer (actually referer as it was incorrectly spelled when it was added to web protocols), is a CGI variable available to methods. I can formulate a PHP cURL request or an internet explorer request that, as it loads a page, emulates the referer variable. So then, with 1000 proxies ... I could trick analytics into thinking that 1000 different people were visiting your client's website, and fake Google as a referer as I sent my request header for the page.
For a proof-of-concept, I'm sure if you google it there's a firefox plugin that would allow you to simulate a referer as you load a page. Change your proxy in firefox. Load said website, boom you just faked a referer that shows as visit from Google in analytics.