Used phone don't really have interresting price (the Nexus4 cost around 340€, used it cost 300€ and it's still 80€ more than a new one in US ...) , i would rather buy a new one with 2year warranty than a used one who can brake anytime.
But we do have website or store for used goods and also ebay, i bought all my bikes on those kind of website. But... i don't like the idea for electronics ( mainly because I don't have the knowledge to repair it if there is a problem ). Also I try to keep my device as long as possible, my blackberry have 3year and a half now and i hope it will work till my amazon package arrive. So in my point of view used phone is not my cup of tea
What i found about Ghostery isn't really cool → A Popular Ad Blocker Also Helps the Ad Industry | MIT Technology Review
I use to have the noscript implemented in chromium active but i was too invasive in my browsing experience ...