I'm not at all surprised that the listing agent is saying you need to submit an offer to see it. A short sale approval by the bank can't even begin until they have an offer to submit to the bank. Often times the short sales are listed quite a bit lower than the current market value, which would bring tons of people through your home, all of them aware of your humiliating position of having to short sell.
Once the short sale is approved by the bank, I"m sure they will gladly show it to seriously interested buyers. If you submit an offer it's meaningless unless the seller accepts it, which they can't until the bank OK's the deal. Assuming your offer is accepted, that's when your contingency period begins. I believe the standard is 17 days from acceptance you sign off on the inspection.
If they do accept your offer and you look inside and decide it's not what you want, then yes, you can rescind your offer. If you do like it, then you need to get an inspector in there to check everything out to make you aware of the condition of everything. The seller being in a short sale position is not going to throw any money at repairs. So you will have to decide if the cost of the repairs still makes the price right for you.