Try to cancel the transaction if Paypal gives you an option! If not, contact the seller immediately and try to work it out with him. Since he offers them as "100% authentic guaranteed" you can contact him after receiving and let him know that they are not authentic and tell him you have verified this. Ask for all of your money to be refunded and ship them back. Hopefully this will all work out for you
All of that being said...we are assuming that his items are fake because he does not post real pics and the size tag he shows on the listing is NOT his (or if it is, many sellers copy it...and Bianca is right, that tag shown is defintely fake--see the stitched cut number?)! Who knows what the jeans he has really look like...! GOOD LUCK!