As long as people are going short, banks have incentive to keep the price high and rake in the interest, using it to keep inflating the price. Only when everyone has stopped believing the price will go down and stops short selling, then the banks can no longer inflate the price and will let it go down. See oil for an example.
During the first 30 days after an IPO, the underwriters are not allowed to lend shares for short sale. Additionally, number of shares are limited. The entire float is not available on the first day of trading. So today, it is probably impossible to short. 30 days from now, it should be available to short.
I've heard that larger banks and brokerages (not the underwriters) will start making shares available for shorting as early as Tuesday, which should help ease the share price down.
Not always. There are some companies that don't have enough liquidity to effectively make that trade or have no investors willing to lend the shares. Not to mention shorting (or options) aren't even allowed yet on this particular stock.
Welcome to the rigged game.