Of course we are all here always telling our banks and our governments and all agents the truth, I though that was implied haha 😉 This is why we are on this forum so that we can learn how to just tell the bank the truth in the best way.
I think the question implies: what kind of documents does an average bank want to see when they say "source of funds"? Simply an invoice for some service? Are they ever checking these? How, do they call︀ people on the invoice, do they check company numbers?
Or do they want other documents︁ besides an invoice too, like some proofs or pictures of the finished job/service?
In a︂ generic case, what kind of documents will make the bank sleep well for a 500'000$︃ transfer for example?