I've been using Ebay since 1995/1996 and PayPal for a least a dozen years. PayPal has been owned by eBay for many years now. PayPal works by linking your credit card or your bank account to the PP account.
When you buy something and pay via PP, they charge your bank account or credit card and send the funds to the seller, thus PP becomes the merchant of record as it pertains to you or your bank. PP then puts the money (less the seller's fees) into the seller's account. The seller then ships you the item.
As far as I now know, PP is required to buy and sell on eBay. Back in the day, check or money order could be used, but PP is a safer way to pay. If there are any issues, you get your money back fairly easily from PP and then it is on them to get the refund from the seller. With the old school check or money order, your ability to get a refund basically relied on the trustworthyness of the seller and how badly they wanted to keep their ebay feedback clean.
As far as risk with a credit card, get a low credit limit card that you only use for PP/eBay. You know the ones you get pre-approved in the mail every Wednesday. Set the limit at a few hundred dollars and pay off your balance every month. It will be easy to detect if the number gets compromised and if it does, the damage will be minimal if the card gets maxed out quickly with such a low limit.
I've never had an issue using PP. Any issue I've had with a seller involved delivery issues, but I've never not received an item I paid for. I have had sellers send me the wrong item. One time, I forwarded the package for the seller to the proper buyer and the seller reimbursed me for postage. Another time the seller (a Hong Kong hobby shop) sent the proper kit and told me to keep the wrong one. I guess it was less money to just write it off than to pay me to send it return postage due to HK.
There is a Model Kit category on eBay. It even breaks down the category into 17 subcategories. Everything from Aircraft (non-military) to Super Hero to Wooden kits. Several of the subcategories, like Military or Sci-fi, are broken down even further to various sub-subcategories within that genre. For instance, Military is broken down into Armor, Air, Sea, Figures, etc. Sci-fi is divided into Star Wars, Star Trek, and other popular areas.
http://www.ebay.com/sch/items/Models-Kits__W0QQQ5ftrkparmsZ72Q253A1205Q257C66Q253A2Q257C65Q253A12Q257C39Q253A1QQ_catrefZ1QQ_sacatZ1188QQ_sopZ1QQ_scZ1?_trksid=m194&ssPageName=STRK:MEFSRCHMODX:SRCH