If selling it to an individual then 100% would equal 1500 gp, if selling it to another merchant, then the merchant is very likely not to pay more than 50% to 60% of the 1500 gp.
However, don't forget the modifiers -- with a normal cost of over 1000 gp, that gives it a -100 on any trading rolls. With the -100, it would take a roll of 251+ to get 100% of the 1500 gps. On average, they are likely to not get more than 50% of the value.
As for the Scimitar -- have somebody take a swing at something (that has DB). After a few swings, they would tend to know how good it is.. (i.e. what the bonus is). This sort of testing can also be done in sparring sessions, as it is a constant bonus, so it needs no attunement.