On a couple of occasions after I've had some communication already with a seller (clarifying questions and the like), I've asked if they might consider an offer. I think it's mostly a matter of personal integrity. I try to make an offer that is both reasonable to the seller but still somewhat favourable to me, and make it clear that if the seller doesn't wish to accept then that's no problem, I'll bid on the item regardless. The way I see it, as long as you're not seeking to deceive the seller or undermine their sale, there's no harm in making an offer and trying your luck. I do, however, prefer to make contact via personal message or email rather than asking publically. I think that's more respectful towards the seller and the auction process.
I haven't purchased anything shaving related for a while. I made a pledge to myself that I wouldn't buy anything new until I actually finish something, but I'm going to Sicily in a bit over a month and I've hunted down a couple of barbershops there, so that'll be my thrifty attitude done.