Originally Posted by
bennos
I'm going to vote "moderately shady". DL advertises a flight with availability at 25k or $330. It's completely unintuitive to the average person that purchasing with miles would cause the cash price to change, or vice versa, and in fact the implementation is explicitly designed to make it difficult if not impossible to do. eg: A customer friendly implementation would allow you to book both tickets at once.
You could book both at the same time (at the higher price). However, the OP was using two different FOPs (miles, voucher+cash) so that isn't an option on any airline that I'm aware of.