Been there, done that, got the t-shirt
I initially lost out in the rush for Google I/O tickets and ended up going through eBay for a ticket which I got at 'only' three times the list price. Ironically that makes two days at Google I/O the same cost as two days training in the UK. Oh, plus travel and hotel. But you won't get Google I/O anywhere else anytime soon.
I proceeded with utmost caution after winning my auction and was able to confirm with Google that my ticket was genuine, and correctly transferred to me, within 24 hours of paying. I hate working in this way but I'm not sure what the best solution is. Supply and demand - when demand far exceeds supply, touting is inevitable.
If purchasers provide some kind of ID when purchasing - credit card number is probably best - and must produce the same when registering at the conference, and a photo ID in the same name (passport, drivers licence) then this would kill enough of the touting to make the rest not worth chasing. Add in the rule that anybody who turns up without the prescribed ID (and therefore isn't let in) gets a refund of the face price of the ticket, and the ticket then goes to somebody else who's pre-registered for a physical ticket returns queue and actually shown up on the offchance.
If you want to return your ticket in advance then this should be possible for free. Google (or Apple, or whoever) refund, and assign the spare ticket using something like first come first served, or a lottery, of people who have registered interest in returned tickets.
in the absence of this kind of arrangement: just make it clear what the criteria for getting in on the day is, make sure that 99% of touted tickets won't be valid on the day (we're back to ID again), and don't try to police the touts. Just put out lots of publicity that a touted ticket is invalid and won't be honoured.
Google were very clear when I contacted them about purchasing through eBay, academic tickets cannot be upgraded but beyond that anything is permitted. Provided people know what the T's and C's are, and are careful in their approach to verifying their eBay purchase, nobody should get ripped off (beyond paying over the face value of the ticket).
For the record, if I miss out next year, I'll go back to eBay to get into Google I/O. Perhaps these companies should consider running their events in more than one continent (e.g. North America, Europe, Asia, Australasia) and just repeat the conference in several locations over several weeks.