On 30 May, 22:18, Michael Hoffman wrote:

Well you'll have your shopping on you, so that's one way.

Another way is if you were caught not touching in or out by an
undercover inspector. Or if, when questioned on the train about your
anomalous touch-in, a witness stepped up. Or they could have CCTV tapes
checked if there are any.
--
Michael Hoffman

Yes of course, you can use these methods, but i suppose it's unlikely
they would just check andy analyse CCTV footage to check who didn't
touch out, and then to try to find him not touching in. Also, in
Canary Wharf station, there are just so many Oyster readers all over
the place, that undercover inspectors job would be extremely hard.

Shopping is a good point, but you can always put stuff to your
backpack (which I usually do)

Also, regarding to time limit, I found this:
"The two-hour Maximum Journey Time (MJT) was determined when Pay As
You Go (PAYG) was launched on the basis that Journey Planner didn't
quote any journey on the Tube and DLR taking longer than this." -
http://www.ealingtimes.co.uk/oyster/weekone/

That means that I can go shopping or just walk around for more than an
hour for the price of a single fare