Sorry to hear of your problems.
There are a couple of issues that you should be aware:
First, contrary to what you might see in the media, underwriting standards are tightening. It is not uncommon for a buyer that is qualified at one point, with NO change in their financial status, to become unqualified.
Second, it is the listing agent's job to keep track of the buyer's financing. As an example, it is legal for you, the seller, to require that the buyer "co-app" or apply to another lending institution as part of the offer acceptance. Having the buyer applying for loans from more than one lender, particularly a lender that the listing agent knows well, can really be a big help and perhaps avoid problems like yours.
Third, it is not uncommon, even in the "normal" times of the recent past, to simply have lenders make mistakes. The Calif. Association of Realtors conducted a survey that showed that about 37% of the time escrows fail to close on time, and 70% of the time it's because the lender made a mistake. So it is widely known by top agents that having a firm handle on the buyer's financing is key.
You should make sure that you ask your Realtor the questions you asked us. I am concerned that the sale took so long.
The key question I would ask your Realtor is this:
SInce our home hit the market, how many homes, like ours , have:
Come on the market
Lowered their price
The proof will be in the numbers.