Of course it is possible to use Betfair for surebets. It is only a question of the construction of such arbs. You need to do crossmarket arbs. For example "more than x goals", "under x goals", "correct score" etc. Here one example:
Correct Score 0:0 plus 1:0 plus 0:1 is the same like "under 1,5 goals" which can be combined with "2 goals or more" or in a tennis final, the "tournament winner" is the same like the "match winner" (which can also be combined with a nice "set"-bet...there are dozens of such combinations...watch an inplay game like soccer and you will discover such possibilities...
for me it is too fast, thats why I personally dont do it