I need to say that the last comment about Conch coming across as trying to find an excuse to keep your security deposit has really rubbed me the wrong way. In my mind, there should be some proportionality between the age of the boat and the invasiveness of the post-charter inspection. If you're chartering a new or pristine "premier" boat, I can expect the company to make a pretty close inspection. But as the boat becomes older and more beaten up, these invasive inspections can seem more and more unfair, because it's much more difficult to discern actual damage from normal wear and tear.
All I can say is that I have chartered from Conch twice and friends have also chartered from them and that is not my experience. Sure they check the boat over when you return but you'd expect that - at least they didn't charge us when we lost a towel.
Last time, we had a crew injury and had to go back to the base a day and a half so we could get her medical attention and they couldn't have been more helpful and understanding.
After talking to Conch, I think I'm probably going to go with SunSail because I'm considering a week that they have a 25% discount that puts one of their "premier" boats in the same price range as Conch's older boats.
I'm a cheapskate so I always check the prices and, at the times that we want to go, I have always found Conch the best. I like Conch but if I could get a newer boat for less, I'd go for it too.
As for reliability, sure the boats are older and we have had some very minor problems but nothing serious and nothing that needed anything expect to let them know when we got back. The only time I've had a major problem with a charter boat, it was in the Abacos with a year old Moorings boat - boats can be unreliable and sometimes things break.
If you do go with Conch, see if you can get Irene to do the briefing - she's by far the most informative.
Most importantly, relax and enjoy