Unfortunately, they are probably not worth as much as you might be hoping. It will depend a lot on how much they have been used. At nearly 10 years old, I'm guessing that they will have been used quite a lot.
The thing is, Farr40-OD is one of the very competetive one design classes
. As a general rule
, boats replace their sales fairly regularly, so you really can't be competitive with old sails
(which is probably why you have inherited these). The top boats get new sails every year. Even in relatively lower-key fleets, it would be unusual to see sails being used that are more than 3 or 4 years old.
Also, there are not really any "cruising" F40-ODs, so there isn't really a big market for used sails. As you probably know, it is not generally good economics to make significant changes to the size of an old sail because you end up with a poorly shaped sail that probably isn't going to last all that long anyway. So, unless there happens to be a whole heap of cruising boats out there that just happen to have the same headsail sizes as the F40-OD, they are going to be hard to sell.
Finally, bear in mind that F40-ODs run non-overlapping headsails, whereas most cruisers tend to run big overlapping jenoas. And, since these are probably regatta
sails, they aren't going to be heavy enough to make #3 or #4 non-overlapping jibs.
Sorry if I have sounded rather negative. I hope I am wrong. You might be lucky and find a F40 that wants some training or beercan sails. I think your best bet would be to contact local F40 owners and ask if they want old sails or know an owner who might.