Over the past few years, I've foregone the boat payments and instead chartered. I've had great, good and not so good trips. Guys often determine good/bad by the number of fish caught, but that's not always the case. It's sometimes a shot in the dark fishing a new place, but there are a few things I look for.
1) Captain is knowledgable but listens to what you are interested in and works to put together a plan and does a good job of explaining the strategy. LISTEN TO YOUR CAPTAIN TOO! Chances are, they know a lot more than you do about the places they fish, and aren't reading the same ficticious or week old reports you are. I look to learn from these guys every time I go out. There are some out there who could care less about tides, whats biting when, etc. They want to leave at x, drift the race, and get back at y regardless. I can go on a party boat for that.
2) Like being out there and get pumped when clients catch big fish. Some of the best guys I've gone out with share knowledge, tell great stories, and will tell you that the biggest rush for them is hooking people up with the target species. 4-10 hours on a boat with a guy that acts like he's having about as much fun as working a production line makes for a long trip.
3) Thinks "out of the box" and will change up the game plan on a slow day. Sometimes the fish don't seem to bite but a good captain will at least try a bit of everything. There are days when everyone gets skunked, but you know when a guy has busted his ass trying to get you on the fish, and that's a guy I will fish with again.
4) Big for me - wants to preserve the sport. Is ethical in methods and works to preserve the stocks. Believe it or not, I hate to eat fish, so I catch and release unless I want a few fillets for friends. Perhaps my coolest fishing moment was at the end of landing my one and only marlin, brought it to the side of the boat to snap a few pics, and then cut it loose. The fish and I were spent, and that thing just glided back down into deep water.
Anyway, thought I'd share. Maybe even help someone looking to charter. If you need an extra to split a share with, send me a PM!