In most cases this can work very well. You can quickly be shown areas of the lake that hold fish and more importantly how to run the lake safely. Always be up-front with the guide. Let them know you will be fishing the lake several days or that you are pre-fishing for a tournament. Being honest and up-front is far more rewarding to you both.
Guides work all year keeping in touch with their fish.
I've had whole areas decimated after a guide trip with clients who went back into the areas where I took them and kept and filleted their catch for several days afterward. If you tell the guide you are going to release the fish you catch, then do what you say you will do. Guides work too hard to stay on fish to have them all just fill someone's freezer. I now have some ex-clients who probably wonder why I'm always booked when they call. Another thing to keep in mind is that most guides fish with people who are probably less experienced than a tournament competitor.