basskisser wrote:

It's a shame that the work ethic has evolved to having to bribe someone
to get the service you are already paying for...

Or that the human heart has hardened to the point where an annual token
of appreciation
cannot be considered anything other than a bribe, as well as
unneccessary, because, after all, the service was "paid for". We now
encounter tip jars almost everywhere we go.
I have a tough time justifying a tip when there has been no personal
service rendered. I hate to admit it, but when I get to the head of the
line in a self-service cafeteria (where you
gather your own food and are expected to clear your own table) I seldom
feel compelled to drop a buck or so into the jar labeled "college fund"
for the benefit of a surly, disinterested
cashier who doesn't smile, doesn't look me in the eye, and whose only
service is a few keypunches and announcing, "$8.35, please." Some
people seem well suited to minimum wage employment.

Proliferating tip jars may reflect the economic fact that wages in
general have been pretty flat
for several years. Management may be responding to some of the requests
for increases with "Naw, not this year. But you can put out a tip jar
if you want to." Our service industry workers are being reduced to
begging, and that's pretty sad.

The situation with this marina manager is different. He most likely
isn't soliciting tips and doesn't expect a tip in the course of his
daily or even monthly duties. A $20 bottle of booze,
a couple of decent cigars, a pair of tickets to the ballpark, or
whatever else depending on what the guy likes to do is different than
an attitude of "I won't lift a finger to keep your boat secure and
protected unless I am regularly tipped, and the amount work I do on
your behalf will depend entirely upon the amount and frequency of your
tips".

So I disagree that the marina manager is trying to bribe the OP. A tip
in this case would probably be a sincere expression of appreciation for
personal service rendered, not a substitute for an equitable wage or a
bribe to get any service at all.