Alex as we have commented in many posts like this, it is hard but not impossible to get the deposit back. A 20k deposit is worth spending more money with an attorney to attempt to recoup. Your premise is correct that as long as they meet the numbers for prequalificatin, then they will have a difficult time proving hardship. Even not getting qualified from another lender doesn’t help because it is the preferred lender that the builder is working with. Everyone should recall that even if you purchase a home from a builder and DO NOT use the preferred lender, the builder will still enforce that you need to be qualified by the preferred lender.
The bottom line is the post in this thread that talked about being the squeaky wheel. You need to get around the sales people and get to management. You need to start getting things done in writing and producing documentation so that if necessary, you can build a case for litigation. The purchase contracts used by the builders are iron clad BUT they still do not like to go to court. Now you may need to spend another 1k-2k to attempt to get your money back (this is an estimate for using a RE attorney to take some rudimentary steps) but it may be well worth it in this case. Usually people who take charge and do this get the attention from management.