I have been picking up many runeskulls on my travels but most I will not use as it doesn't suit my character or the negatives are too strong. I have looked for places to sell them such as magic items shops and the mages guild merchants yet they never come up in the selling screen.

Will anyone buy them off me?

Runeskulls? I'm not sure what you mean? Are they a vanilla product of the game?

There is no such thing as runeskulls in vanilla.

think its part of FCOM or you can get it as a stand alone mod. probably cant sell them. they do look pretty bad ass though

Yes it is part of FCOM and is a standalone mod as well. I figured they may be a popular option among PC users. So you don't think I can sell them? That would be a shame as anyone who would be interested in buying magical stones would want them.

Try a general merchant. If he wont accept it then it might be safe to assume they can't be sold