Some sites, such as William Hill, offer a range of different sign-up offers. If you just visit www.williamhill.co.uk it's quite possible you'll be offered one of the myriad of different sign-up promotion codes. When I visited the site this evening, it was a £20 matched deposit.
£20 in free bets isn't bad. But a quick Google search for "william hill promo" turned up their C30 promotion code, which returns 3 x £10 free bets for a £10 deposit (the url was http://static.williamhill.com/sport/betting-30/?var6=ukggsport6157_ad001&gclid=CO2u36an6NACFY0aGwodB8oBfg&gclsrc=aw.ds ) so if there's an extra tenner going for nothing, it'd be silly not to take it, right?
So my "qualifying bet" was £10 on Lazio (against Sampdoria on the 10th Dec 2016) at 2.5. Instead of Betfair, I used my second betting exchange account Smarkets and placed a lay bet for £10.25 against Lazio, with odds of 2.46
This was one of those rare occasions where the qualifying bet didn't actually cost anything to place (I'd normally accept up to £1.50 to place a qualifying bet to get £20-£30 in free bets - in this particular instance, irrespective of the outcome, there's a 4p - 5p profit on the qualifier!)
The three free bets were credited immediately.
Well, Saturdays are usually pretty busy times with lots of football and horse-racing. But it's just gone midnight at the time of writing and the number of "close matches" between the bookies and the exchanges is pretty low. So instead of trying to squeeze every last penny out of the three free bets, I'll just take what's on offer, and go to bed!
The first free bet was placed on a 1-1 scoreline in the Everton v Watford game at odds of 7.0. Over in Smarkets, I got to lay the bet for £7.92 at odds of 7.6.
The second free bet went on a another 1-1 scoreline, this time Rochdale v Scunthorpe at odds of 7.0 as well. There wasn't much money in Smarkets for this game, so we had to lay it on the Betfair exchange, putting £8.39 at odds of 7.2
Another 1-1 result made up the third and final free bet - again at odds of 7.0, this time on Notts County vs Wycombe Wanderers. Again, Smarkets was pretty bare, so I stuck £7.95 against the 1-1 result on Betfair.
With the three free bets placed (a total of four, including the qualifying bet) all resolving the next day there wasn't much else to do, other than go to bed, forget all about the results - and check Betfair some time after 5pm on Saturday, to see where all the money ended up!
EDIT (three days later):
This is where things can (sometimes) get a bit sticky. Lazio won!
At the end of it all, my three free bets lost - so the "winnings" from those bets appeared in my betting exchange accounts (Betfair/Smarkets). But the initial bet won. With £10 at (decimal) odds of 2.5, that meant I now had £25 in my William Hill account.
Not a problem - just withdraw the cash and move on.
Except William Hill were reluctant to release the funds. They didn't say I hadn't won, nor that I couldn't have the winnings. But when I tried to withdraw the money back onto my debit card, they said there was a fault and that I'd have to request a bank transfer.
I requested a bank transfer and after waiting 24 hours, was told it had failed. The name on my bank account (Mr C Holden) did not match the name on my William Hill account (Chris Holden). I got onto support and they simply said to re-submit my withdrawal. I did this. Twice.
So after three days of still not having the cash, I decided to "lose" the William Hill balance into the exchange account. I put £25 on an obscure fooball game - Atletico Tucuman vs Quilmes - for a result of more than 3.5 goals. As long as there were fewer than four goals in the game, everything would be ok.
Luckily, the final score was 3-0 so my bet lost at William Hill, and won at Betfair.
As most matched betting results in a small loss, I didn't quite get my full £25 back, but enough of it to get out of the promotion and move on to the next promotion.
Total income from the William Hill promotion was:
Everton v Watford: £7.76 (£7.60 after 2% Smarkets commission)
Rochdale v Scunthorpe: £8.39 (£7,97 after 5% commission)
Notts County v Wycombe: £7.95 (£7.55 after 5% commission)
My Lazio bet cost me a tenner and after first winning, then "losing" the second bet, total income was £24.34 (£23.85 after commission) which means my qualifying bet cost £1.35 (usually the initial qualifying bet costs a few pence or a quid or so, but in this case I managed to find a match that made a 4p profit)
Total profit on this promotion = 7.60 + 7.97 + 7.55 - 1.35 + 0.04 = £21.81
For all the matched bettors following this, that's a 72% return.
Not quite the 75%-80% most people aim for. But it was quick to get through and I had to deal with the extra issue of placing a fourth "losing" bet in order to get the cash out of the promotion. In short, it was nearly £22 for about 15-20 minutes total effort. Good enough for me!