Maybe just make a random listing , something no one would want , don't include a pic & and i'll bid 500 on it , once the bid for that listing is over you can keep the 500 while in the meantime you send over the 50 cards ?
Sorry my friend, its not worth it. 500 credits is pfft [you get 500 without lifting a finger on here]. The postage alone on these is about $2. They go for about 1300 for 50 on the low end, I can do this all year long with 3000+. Sorry but 500 for 50 is not worth it.
No Dark Magicians that I know off, and very limited number of rare cards, as I mentioned before those were mostly taken out for auctions I was running last month.