What's the (unobvious) meaning of "I saw you coming"?

Watching an episode of Ruddy Hell, the phrase "I saw you coming" was printed on a shop and the shop owner used it when talking to the rich lady. The context was that he sold stuff second hand and even openly admitted that it was only worth "a fiver" when he bought it. He then exclaims: "But I saw you coming ..." which apparently is the excuse for a much higher price when selling.

Now, I get the approximate meaning from the context, obviously. However, how would native speakers explain the exact meaning of the phrase?

Solution 1:

This is quite a common phrase where I'm from...

'Saw you coming' is used to somewhat comical effect and what you saw was a reduction to the asburd - this would never be used in that context but instead, say, among friends:

Friend A: Check out my new branded watch, it only cost me £100!

Friend B: They saw you coming, it's a fake! [laughing ensues]

In this sense, what 'Friend B' is trying to say is that the seller would have known the watch was only worth, say, £25, and to somebody else may well have sold it it for such a price; but 'Friend A' was naive, or for whatever other reason, the seller had made a prejudgment (and preparations) based on experience which saw him trick you into paying a higher price.

The bottom line is that you were played, cheated, gazumped etc.

Solution 2:

In this case the extra meaning comes from the idea that if you see a particularly gullible person coming towards you you might raise your prices in order to extract the maximum possible value from the transaction.

Alternatively it could be that he is blackmailing her because he saw her "coming" (and implicitily recorded it).

Solution 3:

In the Black Country ( a region of the West Midlands ) "To see you coming" means that you can be easily fooled.For instance if a man bought something & paid over the odds you'd say to him "They saw you coming"