2018 F150 question - tape residue on back window
 

Hi everyone, thinking about buying a 2018 F150 XL Crew cab 5.0 FX4 - went and looked at it today, and one thing has me scratching my head...

Tape residue on exterior back window on various locations: one piece of each side, and one on each side of the bed light/3rd brake light. Is this a sign that that back window has been replaced by the dealer?

Any way to know for sure?

Also, since I'm here MSRP is 46,900 or so, would getting them down to 36k after rebates be a fairly decent deal?