It's certainly possible for standards to slip after a few visits but there are many factors at play and many potential outcomes.
1) WG sees she's getting a repeat customer, thinks "thank God, an easy one, he's a nice reliable pay packet" and delivers a perfunctory performance. Punter leaves feeling slightly cheated. I imagine this is what a lot of punters must assume.
But it could also be:
2) The WG is having an off day. The punter sees her, compares back to the good first meet, and with a sample size of n=2 confidently declares the WG is a lazy bint who has him marked as a sucker. Indignant, he never sees her again and thus his opinion goes unchallenged.
Or even:
3) The WG provides a consistent service. The punter feels that a few meets in the SP should have "loosened up" and started offering discretionary services. With the novelty factor gone, the punter percieves a drop in service, and ups sticks.
On the flip side, potentially:
4) The WG remembers you and what gets your juices flowing, and as a result the sessions actually get better with repeat visits. Happy days!
YMMV.