An exceptionally clean,complete and original outboard motor commands a premium over the
usual run of the mill example that is none of the above. They just look right in the setting you describe. For motors that are to be used, a complete tear down to replace
seals, check and service magneto, clean out fuel system including carburetor, replace impeller and water pump seal is best. Probably only a partial list to things needed.
Value is hard to say because it is between buyer and seller to establish what a given
item, at a specific time and place is worth. Outboards change hands for less than and
more than what an independent party might think fair.
If you question this, see my widow and ask her how much she will pay you to clean out the basement and get rid of all that old junk.On the other hand, an auction venue like
ebay on occasion will reach the other extreme plus S & H.
If seller still has the paperwork that is a plus as would period accessories.