I'm glad you're happy with the deal you got...I hope you'll update us once the shipping is complete and let us know if you ended up with a healthy female on schedule.
However, just based on this alone, and not going by any other history, I would NOT do business on such a recommendation. Sure, anyone can make a mistake and send out the wrong animal...it's bound to happen from time to time. But as a seller, if that were my mistake, I would immediately fix it at NO cost to the buyer...either by shipping out a female and letting him keep the extra male...or by paying for the shipping of both animals...whichever seemed more practical.
You said you made the offer to pay return shipping yourself just so the deal could be taken care of "as smoothly as possible." Does that mean that even with your apparent trust of Dan...you still didn't trust him enough to do the right thing without a lot of drama, delay, and/or emotional abuse?