Something I've been looking at , and finally had a go at today. I think the idea could have merit with many different methods of selection or ratings but in my case my original selections are pre post favs.

The initial idea is to back the selection @ top fluc or if at MR or SR @BOB well b4 the race.

OK so now if 1st or 2nd fluc are better than the original Pre Post price one can choose one of 2 ideas, first, just let the bet ride, as statistically Pre post favs overall will lose about 15% on T/O so if you have secured better than that that then you should win overall, OR you could make a book on the first 3 or 4 rated, as you already have a minimum price on the fav.

Now if 1st or 2nd fluc is below the pre post price, then you can lay off on betfair without too much damage or even a slight profit (in many cases)

eg today at Ascot race 2 pre post fav race 2 -1 $4, Top Fluc = $7

Yes, it's kind of what I do laying, but in reverse.
I did a very long study of bookies fluctuations and derived some very good information out of it.
However there were some caveats on the findings regarding transitions to real time.
I needed to consider what would be matched and what wouldn't on Betfair.
Some of the "if" statements were too pure to be accurate.

For example, if I backed every firmer at top fluc or better on Betfair, I'd make a killing. But the practicality of it is lost, as some horses fluctuated up and down and some of the time I'd be backing horses that later blew out.
This reduces the edge significantly.
Then by the time a true firmer is fully known, the edge has somewhat evapourated on Betfair after commission.

I did however, find it extremely effective laying several "sniff of firming" horses at once forming a part book, that would leave the true firming horse layed at a lower price.

So a practical example of my laying strategy:

Bookies

Horse A $2.00 $1.95 $1.90
Horse B $5.00 $4.50 $5.00
Horse C $9.00 $8.00 $10.00

My Betfair matches

Horse A $2.00 $1.95
Horse B $5.00
Horse C $9.00

So the portion of money allocated to horses B and C offset the price taken about horse A and reduce liability, so I've layed horse A at $1.95 (practically).

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Thanks Chrome, yes I think I am still thinking like a "Bettor" rather than a layer, can't seem to shake it off, but I knew I was on the right track,(no PUN intended) lets just take todays sited example, Ascot race 2 -1 Pre post price = $4, top fluc = 7-1, so lay off initial bet of say $100 on bet fair, say at $5.50 (best price) horse wins so $150 in front, extreme example I know, but remember I will be happy with 1% overall profit (because of the the international benefits, YOU know what I mean)