Hunting for 1st pressings


How do I know if I'm looking at a first pressing of vinyl? 
Also, I've seen ads for new, sealed vinyl claiming it's a 1st pressing. How does the seller know that if the album is sealed. 
rockyboy
I agree with inna, first pressinigs almost always sound better. I have even come across a few 'well used' first pressings that are astonishingly good after a cleaning.  I almost always seek them out. In my collection, the first pressings are always more dynamic then later ones, especially most reissues..

Norman
It's always good to have all possible pressings of a same thingie so you can compare and decide. 3 pressings good 5 pressings better. good luck.
A trick I use is if I see it is a record club pressing it is not a first pressing. If you see Crc,Rca or Bmg record club do not buy.