imo u can always fish for information.
say a seller says "rm1000 nego", u surely dont expect the seller to suddenly say rm500 best price... then u already know the seller is just messing about already in the listing.
but in the end, just the seller's loss if ppl see a stupidly high price listed...some potential buyers may not even bother to proceed and ask further...and may just make fun of the seller.

and whatever it is, at least a price is still listed.
seller is also always free to go sell elsewhere, tho most likely wherever they go also it will ask for price.

sure accepted.
of cos ppl expect some form of nego based on price listed... and of cos got occasional lowballs.
again its just their loss if they put a stupid price and expect ppl to nego highly.
and as depending on item...there may also be others selling similar ones...so just seek for lowest one without having to waste time.

for now better just concentrate on those without any price listed.
at least we don't have to be mind readers to know roughly what they are asking for.

the highly nego part etc, if it really becomes an issue, then let the admins decide on if should proceed further with more action.