Not directing this at Guido or anyone else, just generalizing here....
What I've found in this situation is that a) looks will always be subjective to a very great extent, although great looking will always be just that - great looking to the obvious naked eye but b) sub-par performances after stellar ones are often due to the lack of chemistry and rapport established at the front end of any session.
When I read glowing reviews about performance, it always seems that it's never a 30min ground and pound, but at bare min and hour or more, and that the client put some concerted effort, not necessarilly lots of time, but an effort into building some interpersonal connection with the lady (be it through humor or some other means) BEFORE jumping her to start the action.
My personal sense is that many clients often lose sight of the fact that all services aside, these SPs are REAL PEOPLE with REAL FEELINGS, not automatrons / robotic fucking machines, which can certainly have an adverse effect on your session the more you trend in that direction.
Out of context, if you're genial, friendly and easy going with your waitress, more often than not she'll make your meal a memorable experience of fun, quality dining. Treat her like a confederate slave and she won't give a rat's ass if your food is cold, has the chef's snot in it, or gets delivered to the table any time within 4 hours of your arrival....if you act like a jerk, you'll be seen as a jerk, and the service you receive will suck, even if your waitress is drop dead gorgeous.