Contact the seller via ebay messages with pics and they will either send you a replacement, give a refund, or ignore you. A lot of high volume sellers don’t even bother to check and just mark everything as good used condition. If they ignore you just request a refund after a few days.
White label Beam is 80 proof and Larceny small batch is 92 so it seems strange that Beam would evaporate since its a 6% different alcohol content. If you normally drink barrel strength 120-130 proof stuff I could see it. Bad seal on the decanter lid maybe?