The problem is the value will to a great extent be determined by what you don't know, that is how much it has been used or possibly abused.
Lacking that information then
- Was it used in fresh
water or
salt water? Minus points for
salt.
- Appearance? Take off the
hood and look closely for: rust or
corrosion (especially around joints, bolt heads, etc),
any evidence of
overheating (like discolored or flaked off
paint, browning on any plastic
parts, warping),
leaks (water stains, mineral deposits).
- Give it a test. Make sure the seller has not cranked it recently so the
motor is stone cold. Does it crank on the first or second pull? Any smoke? If yes, what color and how much? Do you see a good stream of
water from the pee hole?
- You say used only 2-3 years but is that also the age of the
motor or has it sat in
storage for some time?
Not sure about prices in
Europe, what with VAT and such but in the
USA I think with a little
shopping you could find a similar engine for less. With a little luck possibly a lot less.