"Why do most carp suddenly refuse instead of just inhaling my fly?" - was the number one question.
Fair to say, this happened to me, too - especially with the bigger (smarter) ones. Carp learn quickly how to avoid getting into some stress.
The more fishing pressure there is, the more our strategy depends on it's details.
Make sure not to offer your fly in the same depth of water in which most anglers offer their bait. Usually having a lot of "boili-anglers" around the lake this often means not to drop the fly on the ground but present it on (or close to) the surface instead.
Offer a fly presenting something new to the carp - different from what most anglers present.
Don't fish at the same time when the fishing pressure peaks. With boilie-anglers that often is evening into the dark. The middle of the day easily can be a very good choice here. Believe me more carp as you may think, are best catchable in the middle of the day when the fishing pressure peaks in the evening! Early mornings can be fantastic as well.
Finally most important: Make sure to have the carp swimming to the fly, not the fly dropping in close to the carp! That to me was the by far biggest "game-changer". Seems to be easy - but it often is exactly opposite! That is because it takes nerves to wait another half hour watching the BIG fish right in front of you to come into the perfect position instead of just laying down another cast...
Some easy key points that taken into account hopefully will help you to get linked to some of these fine fish. Fly fishing for carp has entered my favorites. It offers a lot of challenging moments and pretty strong fights.
Fine fishing week to all of you!
All my best
My last days - all about fly fishing ;) ...