Definitely. I’ve only seen/heard it once. Entering at Suvarnabhumi last month I was annoyed that some people in my queue took what seemed like ages talking with the female IO. Eventually, another IO appeared and took them to the back. Previously, I’ve only seen the odd person pulled out of the queue. I counted three that time.
Immigration do ask for sight of cash. I overheard a guy in the adjacent queue at Suvarnabhumi Airport being given a hard time. I was quickly through and away so don't know whether he was permitted entry or not.
The OP now has justification to request a chargeback by their bank/credit card company. Singapore Consulate requested additional information from another applicant. This they neglected to do from the OP and simply rejected their application instead. Complete lack of customer service.