Now, if you see something with SPF, you can always contact the seller anyway stating that if the original buyer backs out of the deal (which does happen), that you're willing to buy. But most of the time, SPF will mean it's sold.

In most cases SPF stands for Sun Protection Factor. However when it comes to buying and selling items SPF means Sold Pending Funds.

lol yeah i know what that spf ment too lol tahts why i was questioning cause i know another way of saying sold was by posting banana so i was like hmmmmmm this might be another quirky thing that ppl do on this forum

Crunch has a good point here. If you see something that you really want and it's SPF then there's still a chance you might be able to get it, if the original buyer backs out. So by all means private message the seller saying you're interested in purchasing the product if the orginal buyer backs out. I've managed to get several hard to get items that way.

This mite help you understand more.
http://www.airsoftcanada.com/showthread.php?t=107