I know someone who works for a bookies and is involved in setting odds. It is not uncommon to start playing with the levers manually if you get my drift.
Knock the odds down encourages a pile on. House always wins.
Of course I do mate but 16/18/1 down 7/4 is more than that , also it works the other way Arsenal where 1/10 and 1/16 on in places last night now 2/5