My take. I've tried to go for a natural conversational British English style.Remember that there are usually many different ways of expressing the same thing. Also, contractions are much more natural for spoken language.
A: Let's go over there and see whether they rent kayaks.
B: It doesn't look like there's anybody in the booth. (I found 'guarding' particularly odd here). Maybe they're closed because of the rain over the last few days. It still looks pretty cloudy . I think it's going to rain again.
A: We'll see. I really want to go kayaking. We've already been here 4 days and are going home tomorrow. I don't want to miss this opportunity.
B: We should have paid more attention to the season when we picked the dates. It would have been a great holiday if the weather had been better.
A: Cheer up. Seize the moment.
<B sees a man lying in a hammock?
B: Excuse me, do you work for the kayak hire?/Do you hire the kayaks?/Are you the person to see about the kayaks?
B: How much is it?
Operator: $25 per hour, 3 hours minimum.
B: How about $100 for half a day?/Would you take $100 for a half day? (although your maths is a bit off. 4 hours = half day = $100 at the usual rate?)
Operator: Oh go on then. You guys are lucky I'm in a good mood today. The deal is you empty out the water and stack the kayak on the rack when you've finished. OK?
B: Sure will.
Operator: Also, don't cross the bouy line. Someone drowned the other day and some new rules ban anyone from crossing the line/don't allow anyone to cross the line. Don't get me in trouble.