Super informative post Richard, thanks.
In between trading and other work yesterday I checked back on Betbrain and oddsandbets and there were some tennis matches that offered around 4% for a while but as you correctly point out they quickly evaporated.
One thing that seems to have been touted a while ago is that the prices tend to drift shorter during the day (gee gees) up to immediately before the off, especially on the favourites. Perhaps there is some mileage in backing early and laying at the last moment.
I'll have a dekko and post some initial evaluation.
I agree that although these boards are widely read I do not think the sport betting community are that active here so whatever we discuss is unlikely to affect the market. Certainly, the objective of these boards is to share and help each other make a crust, IMHO.