From Betangel forum:
How can I work out whether s Big Bet is s back or a lay for an automated strategy? Sometimes it’s obvious because the price will change but other times when there is decent liquidity the price won’t move.
I assume there’s a way of doing this because the candlestick charts differentiate.
For any open market selection, bfexplorer app records history of offered back prices, and traded price and volume, in 60 last points, changes.
Bfexplorer app is able to retrieve exact traded prices and volume for last 10000 points as well. This data differs from previous one which depends on set refresh rate of market data update, this data presents any traded price we can see in betfair charts.
So we have got different data and different approaches we can use to detect any extreme changes in traded price, and so when change is positive, the selection was lay-ed, and opposite the selection was back-ed.