Calling stations are certainly one of the most profitable types of opponents you will ever meet at the poker table. Their weakness is that they call too much, and also tend to be pretty passive. So they don't really like to fold, and they don't do a lot of betting and raising either, at least as a percentage of their overall actions.
What we don't want to do though is just look to characterize all players who are on the loose passive side as calling stations, and then rely on a common set of strategies to use on all of them. Players are calling stations by degree, meaning that some are looser than others, and some are more passive than others.
So while there are indeed some common approaches that we want to use against calling stations, the degree in which we use them will vary according to how much they exhibit the particular weakness that we are looking to exploit. For instance, the more times a player tends to call, the more often we'll look to get involved, and with players who play less hands but are still on the loose side, we'll be playing less against them ourselves.
So we know that while these players are loose, they aren't particularly aggressive. So this means that we can more safely bet into them with less risk of getting raised and needing to fold. This is a significant advantage and is one of the reasons why playing passively is weak.
Calling stations play both strong and weak hands. With their strong hands, they tend to want to bet them, and perhaps even put in some raises if they are particularly strong. This serves to telegraph their holdings quite a bit, as opposed to their lesser hands where they tend to want to check and call more.
So this gives us an opportunity to get free cards to draw out on them, and also to be aware when the normal range that we would play against them based upon their looseness may be behind, in cases where they are playing their hands more strongly.
Since they do play more hands overall, and also like to show them down, we will play a stronger range than they do and then look for them to pay us off with weaker. This is the standard method of milking calling stations, although you do want to pay attention to their degree of looseness in general, and together with comparing their standard level of aggressiveness with what is being shown in a given hand, we will be able to put together some good reads here.
So as a rule we will want to play better hands than they do, meaning playing tighter than they do, but at the same time we don't want to play too tight either. If we are alone in a hand with them and are ahead more often than not if called, then it's worth our while to bet.
Given their passivity, we are able to leverage our position on these players even more than normal if they tend to bet out of position with their premium hands. Without position, we can look to check to them and they will also tend to want to give us valuable information. Since they don't bet that much, a bet from them will indicate a stronger hand than normal and we can get away from our more marginal ones when that happens.
Since calling stations like to call so much, we also may be able to get away with their calling larger bet sizes when we have a hand that merits it. These players don't tend to be very skilled so we often won't even have to worry about our plays being too transparent, although we should still look to mix things up here as to not to make things too obvious, or even just go with a bigger sized bet against these players in general, like full pot or even larger. We don't have to worry about pricing these players in since they tend to price themselves in without any help from us.
While taking them to value town is going to be our main weapon, we also want to be aware of opportunities to take pots down against them as well. For instance, some calling stations will chase a lot of draws and will tend to give up on the river when they miss. Or perhaps they are real loose on the flop but tighten up later. So this is why it pays to have good stats, although just watching them will often be enough to spot these trends.
Overall, calling stations can be a gold mine and take the least amount of skill to beat than any other player type. All you really need to do is play good hands against them to make quite a bit of money off them over time, although the more skills and tricks you have against them, and therefore the more refined your play is against them, the better you will do.