I think
serfty is suggesting that the search process could be drawn out to take several hours.
I would expect they are able to ask any questions they feel are relevant to be used to determine if you are in breach of any immigration, customs or quarantine laws. So in some cases it may be relevant for them to ask about how your trip was funded as it is well known that many drug runners are low-income people whose trip is paid by someone else. So if they are suspecting a person of being a drug runner, the source of funds for the trip may well be relevant to help them clear a person of that suspicion.
Personally, I would not go down the refusal path as that is certain to increase any suspicion levels and likely to result in a very thorough search process that may involve more intimate details than your income

.