The problem might be that TradeHill adds orders to the Orderbook before processing them.
For example, this happened today:
Around 18h10 UTC, the highest bid was 4.842524 and the lowest ask was 4.840000
Around 22h00 UTC, the highest bid was 4.820000 and the lowest ask was 4.819900
I have also detected similar situations at ExchangeBitcoins.com. CampBX and ...
Basically, Dwolla promised that they would never honor chargebacks. They in fact did and stole dollars back from their bank account after TH gave Bitcoins to the scammers. They lost a lot of money by this. I believe Dwolla is being sued for 2 million dollars as a result of this.
I recently co-authored an article that contains some background information to your question. William B. Fleming and Joseph Evans, Bitcoiners in the Courtroom Part I: Government Oversight, Ford. Corp. L. Forum (Aug. 20, 2013)
Bitcoiners in the Courtroom: Government Oversight (PDF)
Bitcoiners in the Courtroom: Government Oversight (TXT)
Tradehill got shutdown because it went bankrupt when Dwolla started reversing money transfers made to them despite their terms of service stating that no chargebacks could occur (at the time). There is currently a lawsuit pending.
The required licenses will vary depending on the legal context and the interpretation of the business, made by the relevant ...
If you have technical problems with Tradehill, your first step should be to contact them about it.
It's not clear to me in what capacity you want to replace Tradehill. If you want an exchange then Mt. Gox is an obvious possibility, or any one of the exchanges listed here. If you want an eWallet, most exchanges are good for this too, and flexcoin is another ...