You get a refund of up to £15 on your 1st betif it loses rather than the standard £10.
If you go on to do a total of 10 bets (min odds 1.2, no min stake but must be on markets with at least 3 outcomes) then I get £5. To encourage you to do the other bets I'll give you £2.50 if I get the bonus.
What people have been doing is betting the £10 on something at quite long odds, maybe 11s so they win £100 if they are correct. Then you could lay it at Betfair for a fiver which may have £50 liability. That way if you win at Betclick you are Net +£50 or you are wrong at Betclick then after you get the refund you are +£5.
You can do it 2 ways - either just have a punt on something. If it wins then you've made a profit. if it loses then you haven't lost anything as you get a refund (though you need to bet that through).
If you want to lock in a profit then go for high odds and back and lay the bet. You lock in a profit by laying less than you would if it were a normal qualifying bet - if fact the best way to calculate how much to lay is to pretend that it's actually a SNR bet. ie for a bet that you back and lay at odds of 10 with 5% comission you need to bet £15 at Betclick but only lay £13.57 at Betfair
If the bet wins then your lay risk at Betfair is less than the amount that you win at betclick, so you're in profit. In the above example you've won £135 at Betclick but only lose £122.11 at Betfair so you're £12.89 up
If the bet loses then you initially make less at Betfiar than the stake that you've just lost at Betclick BUT you then get the refund which will put you back into profit. In the example you've just lost your £15 stake at Betclick and only won £12.89 at Betfair (£13.57 lay stake minus comission) so you're £2.11 down BUT once you get you're £15 refund then you're £12.89 up again
As Andy will no doubt point out, you don't need to be quite as exact as in the examples above but using exact figure probably demonstrates the principles better. Betting £15 and laying £13 will only knock 34p off your profit if the bet loses but will gain you an extra £5.11 if it wins
Also remember that the £15 refund is only if you get a referral. If it's a normal sign up then back/lay for a £10 SNR