Over the past couple of months I've listed a number of items for sale on this site. What I've asked people to do is post a message on the sale item stating "I'll take it" and then follow up with a PM to my address stating the same. It's important to do both, place a message on the ad saying I'll take it as well as sending a private message to the seller stating the same. Some buyers have left a message on the ad saying I'll take it but neglect to PM me, while others have sent a PM to me but neglected to post a message on the ad.
The reason to do both, send a PM as well as post a message on the ad is to avoid confusion with both the seller and other potential buyers. When you leave a message on the ad saying I'll take it but neglect to PM the seller, sometimes the seller will not see the message on the ad and not realize they have a potential buyer. If you send a PM to the seller letting them know you want the item but neglect to post a message on the ad saying I'll take it, other potential buyers don't realize you've contacted the seller via a PM and think the item is still for sale.
In short, cover your bases, post a note on the ad saying I'll take it and then send the seller a PM letting them know you've decided to purchase the item. By following this process you'll ensure that the buyer knows you want the item and you'll also inform other members that you purchased the item.
The reason to do both, send a PM as well as post a message on the ad is to avoid confusion with both the seller and other potential buyers. When you leave a message on the ad saying I'll take it but neglect to PM the seller, sometimes the seller will not see the message on the ad and not realize they have a potential buyer. If you send a PM to the seller letting them know you want the item but neglect to post a message on the ad saying I'll take it, other potential buyers don't realize you've contacted the seller via a PM and think the item is still for sale.
In short, cover your bases, post a note on the ad saying I'll take it and then send the seller a PM letting them know you've decided to purchase the item. By following this process you'll ensure that the buyer knows you want the item and you'll also inform other members that you purchased the item.