As far as the legality, I believe there would have to be proof that you acquired the domain with sole intention of attempting to profit from the purchase by mis-leading the customer base into thinking you are related to the .com, or by extorting money from the .com. If you had the domain prior to the .com purchase, or better, prior to a public appearance of the .com brand name, you are likely in good shape, and making an offer wouldn't seem out of place. Your case would also be help if you showed you were building a brand around your .ws site already (content in place, advertised, etc). Im not a lawyer though, so don't hold me to this
They don't have to prove that was your intention, only that it is likely to create confusion. The date of first use of the mark is what matters for infringement, not the date they bought the .com. If the domain registration date pre-dated the trademark usage, it wouldn't be bad faith in itself, but the content on the site could still be infringement.
I Doubt the .com buyer would be interested he has the main domain already who cares about .ws domains but worth a try.
Well if the .com person needed it he/she would have got it before you. so i guess just keep it and have something on it.