I don't know about the Crown 7 cartridges, but I do know that the Ruyan cartridges and njoy cartridges are interchangeable. My guess is that the Crown 7 cartridges are just a tad shorter than the njoy cartridges, so they may not make a good contact with the atomizer.
As for bidding on ebay, you can do it a couple of ways. You can put in a bid for the maximum you are willing to pay and ebay will increase your bid up to that amount whenever someone else bids. You could also just put in a bid for the $19.95 and then keep watching to see if someone else bids over you, and then put in a higher bid. Many people don't bid until the last minute, so you have to be on your toes.
You may want to go ahead and open accounts at both ebay and paypal, if you haven't done this already.
Also, the seller you are dealing with is a very nice lady. If you have any problems, just send her an email and I'm sure she will try to help you out. It's not a bad idea to contact her and let her know that you are new at this. Happy Bidding!
As for bidding on ebay, you can do it a couple of ways. You can put in a bid for the maximum you are willing to pay and ebay will increase your bid up to that amount whenever someone else bids. You could also just put in a bid for the $19.95 and then keep watching to see if someone else bids over you, and then put in a higher bid. Many people don't bid until the last minute, so you have to be on your toes.
You may want to go ahead and open accounts at both ebay and paypal, if you haven't done this already.
Also, the seller you are dealing with is a very nice lady. If you have any problems, just send her an email and I'm sure she will try to help you out. It's not a bad idea to contact her and let her know that you are new at this. Happy Bidding!