Yes - be the first to post in the thread that you will take the knife and provide an email address for the seller to contact you. Be certain to be attentive to your incoming emails and be prompt to pay or the sale could go away from you.
Since you already use PayPal with eBay you have a PP account. Good idea to go to PayPal and follow the links to make certain your account is in good working order - that PP has all the info they need from you. The BF seller will provide info - his/her PayPal email account, for you to send payment.
In order to send payment you will need to go to PayPal and click on
SEND and REQUEST. Type in the sellers email and type in the amount you wish to send. The seller will help if you need some guidance. The seller wants to make the sale and get paid so he/she will be your ally in this process.
As for TRUST - do your homework. Check the sellers
feedback here on BladeForum and maybe even check out their profile page and read some recent posts. You'll get an idea of who you are dealing with. Most sellers here are very trustworthy but doesn't hurt to be diligent. If your little voice tells you to back out - trust your voice.
Since you don't have any buying history and to date, only 2 posts here on the forum, y
ou could raise more issues about trust than someone with hundreds or thousands of posts and lots of feedback BUT as a buyer your only real responsibility is to make certain that you pay promptly and communicate effectively.
Have fun with it and be sure to get a strong rubber band or padlock for your wallet.

You could be going down a deep well of spending.
Welcome, welcome and enjoy!
Ray