if a tipster loses 3 bets out of 4 on a 4.2 odds, he will be in profit still, it is called value betting
you cannot be right 100% of time, but if you make 10-20% of bank long term
you can consider yourself an exceptionally good bettor
with fixed matches, it is never a public information - do not expect someone risk blowing the whole thing up by making it public
bookies are not retarded too and if they see something fishy is going on, the odds plummet or the game is a no event for them
Definitely I agree that you cannot be right 100% of the time, and this is why I don't even really follow tipsters, because they all seem to be showing high percentages of wins against losses. And on further inspection, many of the tips they show are quite low odds, like lower than 1.5 sometimes. And they cannot really show you 10% profits or whatever with consistent gains, just big bets to make up the bank.
Regarding fixed matches, I don't know, I've never experienced a game become no event yet, and since fixing cases only happen years after, can't remember if I ever bet on them!
I am sure last time having so many tipster around with such criteria like veleten said but in the end they just do not post again because lack of time or may be they do not getting any donation or anything in return so most of them are just stopping. Nowadays they are coming back again but only giving short term pick. Never have anything good either for a long term which is I do not really like the result as well. No details about the bet everything, so I do not follow anything, except if there is some big matches going on