Others have given you great advice but I want to add a couple of things to consider.
1) Always elect to have your REALTOR speak with the Listing Agent / Broker and get the updates. The Listing Agent / Broker is actually the person speaking and negotiating with the lender, not typically the Seller.
2) Don't spend any money on an appraisal or inspections unless the full approval letter has been issued by the lender(s) AND SIGNED BY THE SELLER(S). The approval can be issued, but if the Seller does not sign the letter, they can walk at any time.
3) The Seller is likely in financial distress in multiple ways and they do not need or eant any more pressure especially from an aggressive / active Buyer. This will just place more pressure on them and they will push back even more.
4) Is there anything FACTUAL that indicates the seller is not cooperating with the short sale? Is there anything FACTUAL that suggests the Seller is trying to stay in the property as long as possible?
5) Is there any indication the Seller may file Bankruptcy? If so, EVERYTHING STOPS IMMEDIATELY upon the filing and your deposit could be tied up in escrow until the BK Executor releases it. That deposit could be considered an "asset of the BK".
6) If there is ANY FACTUAL INDICATION the seller will attempt to forestall the Short Sale..... You need to GET OUT of this transaction ASAP !
At the end of the day, talk to YOUR Agent / REALTOR and make a contingency plan in the event the seller stops coopperating. On the other hand, if the Seller IS cooperating, you shouldn't be that far away from an approval if it's already been 90 days and the lender(s) have EVERYTHING they need from the Seller.
Best of luck,
Broker / Owner
Thom Colby Properties
Newport Beach, CA
Moving Lives Forward (TM)
We NEVER DOUBLE-END Transactions in our Brokerage. IN MY OPINION, there is NO benefit to the Seller or Buyer and only benefits the Agent.