I know what most tipsters do wrong (and indeed most punters as well) - they look for the horse with the best chance to win but they don't give a damn about the odds. Eg. lets say we have 8 horses in race with the following chances of winning:

1=40%, 2=20%, 3&4=10%, 5&6&7&8=5%

Now most tipsters & punters will pick 1 as the winner with 2 as the danger and 40% of the time they will be correct (or 20% if they go for the danger horse) but what if the odds on that race are as follows:
1=$2, 2=$4, 3=$9, 4=$15, 5&6=$18, 7=$20, 8=$40
Now most punters who dont look at the odds will back horse 1 or maybe 2 but in the long run they will lose money because the odds are worse than the winning chances. The correct bets in this example would be horse 4 or horse 8 because the odds are better than they should be. This is how you get a profit at level stakes and a winning system - you need to find the horses where the odds are better than they should be.