How does the casino spot counters?
In the good old days, counter-spotting was done from the pit. You could /see/ the people sweating your action and moderate your play accordingly. Nowadays counter-spotting is done by the Eye in the Sky, sometimes with the help of clever software. Your play can be closely scrutinized without your knowledge; play intelligently long enough and they will probably figure out what you're up to. The best casinos have computer software which can calculate the degree to which your bets correllate with the count and the degree to which your playing decisions help the house. (One such program is Blackjack Survey Voice). The ultimate result of a computerized "skills check" is a dollar estimate: how much per hour is the house likely to win from you?
Such systems undoubtedly still have flaws, but they are very good at what they do. And the programmers have come up with clever ways to display the results. For instance, suppose you want to know if a player is gaining an edge over the house via bet variation. Do a scatter plot of the amount bet versus the count at the time of each bet. If the player is a card counter who utilizes bet variation, this plot will have a slope; larger bets will tend to match larger counts and smaller bets smaller counts. Even with a lot of cover, mistakes, or deliberate randomness, the slope will be apparent. Whereas a non-counting player's bets are essentially random with respect to the count; the plot will look like static rather than a fuzzy sloped line.