To make this method effective the Geo location of the proxy has to be relevant. It's ok if your keyword is international but there's no point sending clicks from Romanian proxies to a site trying to rank for Dentist Dallas. The proxies also have to have elite anonymity otherwise Google knows it's a search from a proxy. Yes the Google search traffic algos aren't that complex but surely they'd devalue click through rates and traffic from know proxy ip's, especially if they're from another country.
I've also heard that Google have already mapped the entire network of HMA proxies and traffic from their ip's won't register on Analytics, or even if it does, it gets devalued in the traffic algo. (it may be true)
I've also run multiple tests using different providers of Google passed proxies and a lot of them don't register as traffic inside of analytics. All you do is watch your live analytics results while the bots are on your site and you'll see that more than half of the time they're not even counted as hits. I think it's because the proxy is only highly anonymous which means that although Google can't see your ip, they can still tell your using a proxy, and therefor they don't count the hits.
Google passed proxies are ok for scraping but they're very hit & miss when it comes to generating traffic stats inside analytics. Yes traffic and CTR's definitely effect rankings, but just like links, I think the traffic is only as good as the ip it comes from. This means for Dentist Dallas all clicks need to come from the US as a bare minimum, preferably Dallas, and Google can't know that the traffic is coming from proxies, so they need to be elite.
And that's where this serp manipulation method becomes very expensive indeed. Try getting elite proxies in Australia for less than $3 an ip. 500 elite Australian proxies will set you back about $1500 and you need at least 500 of them to make your campaign effective. For the majority of normal local business Seo campaigns you could definitely do some damage with 500 ip's. But then if your using those elite 500 ip's for another client it could leave a huge ip footprint if such a thing exists. What are the chances of 500 ip's hitting the same 3 sites etc. No affiliation whatsoever, but so far I've found Lime proxies to have the best selection of Geo targeted ip's that have elite anonymity and are Google passed.