If you search the group numerous people have been rejected for a wide variety of reasons. Some had mistakes in bio data pages, even though it's automatically input you still need to make sure it's accurate. Others didn't have documents, other applied to wrong embassies or couldn't prove they were in the country they applied in. Many people lost the fee.
all you can do is email or try to contact the embassy on FB messenger and ask why. It could be a spelling mistake, they didn't think you were in the country that you applied to, documents were incorrect, etc. There are a few posts in other groups where people did get the information back, is one case the embassy allowed the same fee to be applied to another application but that seems rare.
Depends on the reason for cancellation and what your original terms and conditions are on the contract... assuming as business you already have contracts in place which state refund procedures? If the DTV wasn't involved and a regular customer quit, what happens?
If there is a valid reason, like no longer physically able to complete, then I'd at least keep a fee for the time, paperwork and refund the remainder as a goodwill gesture. Since it appears that the person just used your services to get approved, I'd keep at least 50%- 75% since your companies name is now attached to the DTV. Again, depends on your contract.
it's not really, don't overthink it. Figure out where you are thinking of applying and check the embassies requirements. If you can't apply there, then look at somewhere else... check those requirements. If you can apply there, arrange travel and get the documents you need organized. The embassy will make it clear if you can apply there or not.
no, for the majority, you apply where you are physically located not based on your home country or residency. Some countries do not let you apply unless you have residency. Every embassy has somewhat different rules so you need to check before you head somewhere.
Book a hotel for a week, get your bearings. Do you know where you want to settle? Spend the time to figure out where you want to live, contact an agent in that area. If you are visa exempt, you'll most likely have to get an agent to help with opening a bank account. If you enter on a NON O, you can open a bank account at most banks. You need a certain amount of time left on your stamp to change in country so don't leave it to the last minute.