The next decision is pricing. As I said, no one is going to pay full price for a used kit that they can get from an online retailer at 25% off. It doesn’t matter what you told your wife about how all your kits will only go up in value, it just isn’t true. Some will over the long haul, but most won’t. Again, scarcity is the primary factor affecting price.
I learned this on my very first eBay sale. I had a copy of the Zotz decal sheet for PV-1 Venturas, of course in 1:72. When I put it up for bid, I put a “buy it now” price as well as a minimum bid price. Personally, I would not do this for any item that you think might generate a bidding war due its scarcity or desirability. The “buy it now” price immediately sets a top end on the potential price. When the decal sheet sold less than an hour after I listed it, I knew that I should have put it on an auction basis. Obviously my set price was too low, which is why it was snapped up so quickly. Lesson learned.
7 day auctions seem to work best. But be aware that the first six and a half days are basically used to allow potential buyers to actually find and see the item. It is relatively uncommon for buyers to start bidding before the auction starts to count down. Most bids are made in the last hour of an auction. One indicator that you can go by is number of page views your item has had and the number of “watchers”, those who are keeping track on the item to be notified when someone bids on it and when the time limit is almost gone. The higher these numbers, the more likely your item will sell.
But be aware that sometimes your item won’t sell no matter if the price is reasonable, the kit is generally no longer available, and you’ve done your best to describe the item accurately. That’s just the fickle nature of the market. Sometimes you have to relist the item, price it a little differently, or adjust your expectations of what the item will draw.