Check the battery switch?
Since I cant see in his boat I dont know if he doesnt have one either.Unless he installed one, there wouldn't be one on a Bayliner runabout.
1) Check the big circuit breaker on the side of the engine to see if it tripped.
2) If you previously disconnected the battery then make sure that you actually put the wires back on the right terminals and didn't forget one. On my 2005 there was a black jacketed wire that actually belonged on the positive terminal - screwed me up a couple times.
I'm assuming it ran when you put it away? Going to have to start cleaning possible corroded connections on the starter or ignition switch.
Yep, clean EVERY connection to include all the ends of the fuses too. If you encounter a copper wire that has turned black or green you need to pay special attention and try to clean it.
When we say ALL electrical ....... that includes starter motor too...... Make sure your battery is NOT connected when you do this maintenance. I usually use a piece of sand paper (I have been known to steal my wife's emery boards from her nail care stash since it is sand paper mounted on a convenient stick)
If it cranks over but does not start then maybe it has a safety lanyard and it is not plugged in...?
Shifter in neutral? Does it act different in throttle only mode?