The bluing stuff in bottles is pretty poor for finishing a gun, it's difficult to get right - easy to smear & give an uneven coating, & leaves a very delicate coating. a couple of unattended water drops & it's gone plus it's pitted. I forget the actual chemical, Selenium? but it's not traditional iron oxide bluing.
I've gone to town with it a few times & concluded it's only for touching up scratches & doing bolts & such.
The going rate seems to be about £60-80 for a traditional finish for a barrel & compression tube, it's hard to see any profit if you're just moving it along but if it's a keeper then contact one of the people on here that do that sort of thing & see what they want, there's a few.