Any one know why a standing bid can not be placed below the market
for nasty seats?
While nonnakip could give you a more official answer, I believe it is due to NastyFans not wanting to hold your funds. You'll notice that you cannot deposit any BTC anywhere on the site, so there would be no BTC backing any placed bids.
When asked about it back in March, this is the answer I gave to cryptocoinsnews.com:
I think we’re probably the first Bitcoin exchange that doesn’t want to touch your bitcoins and charges no fees of any kind. We don’t allow users to deposit bitcoins, and try to handle them as little as possible. For this reason, we don’t have buy orders on our exchange. We only allow sell orders, and when you want to buy, you send BTC to an address specified for that transfer and those coins are bundled up to save on transaction fees, then sent to the seller. It is a limited trust system that not only keeps our users assured that we aren’t trying to amass their bitcoins for a long con, but it also reduces the regulator risk as we can in no way be confused as a bank, and makes us an unappealing target to thieves.