Calvin,
As the seller it's going to be hard to swallow this pill. One thing that your realtor could have done is have his or her loan officer ( Every realtor should have a loan guy or 2 that they work with ) cross qualify the buyer buy looking at the 1003 and grading it to make sure everything looked good.
Now when I do cross qualifies for my realtors the LO might be using a bank that has a program that I'm not familiar with or that I don't offer. In tha case I just straight up ask them can you get this done in 30 days and if they say no ( it happends ) but are honest I'll talk to my realtor and just say extend the COE ( close of escrow ) 5 or 7 days.
After you extend for 2nd time at that point I would just have the buyer start paying for daily interest. If you're saying that the appraisal wasn't even ordered until after the COE that to me is crazy. What was the broker doing for the first 30 days? Now if the loan feel out somewhere else or if the house wasn't up to fannie, fha, va, usda or freddies standards it should be addressed in the sales contract. The LO needs to communicate with the buyers agent and they should relay this to the listing agent so it gets to you.
Sounds like bad luck to me but the appraisal thing is weird to me unless the home had some issues that were being taken care of.
In the future have your realtor's LO do a cross qualify so that expectations are set from the start.
I hope this helps and good luck with all your future deals.