I will try to explain the situation re Fastpasses sold on ebay sites.
To get a Fastpass for certain rides in DLP, you put your park ticket into a machine near the ride, and it gives you another ticket with a half hour time slot to return and enter via the fastpass entrance.It cuts down the waiting time, especially during holidays when the parks are busy. The main queue is usually much longer. You can only get another Fastpass after your time slot, or 2 hrs later, whichever is sooner. It says when you can get another FP ticket in small print at the bottom of your FP ticket. Many people do not notice this.So if your timeslot is in 4 hrs time, you can get another one either for the same ride, or another one, before you use your current FP ( so you are now holding 2 FP tickets).
At busy times, all fastpasses may have been issued for the day by early afternoon, so then you have to use the main queue.
The problem began when people were able to buy Park tickets on the internet, and printed them off as an E-Ticket. This meant they did not have park tickets to use in the FP machines. To get round this, Disney issued everyone with a white ticket just to get FP's. The problem was, that these tickets do not expire, so people were using them again on future trips, and gaining more of them, so they could get more FP's at once. They began to appear on ebay for sale, in packs of 10 or so, so it seems they were also being sold by Disney staff who could get hold of them.As word went round, more and more people were buying them, so FP queues have been getting longer in the parks, with people getting multiple FP's at once.
Disney have now installed new machines where people can scan their E-Tickets, so have stopped issuing the white FP tickets. I have heard that the white tickets being sold on ebay no longer work in the new machines, so they will now be useless.I will try mine in August, but I don't expect them to work any longer.
I hope this explains things.
Reading reviews on Trip Advisor is useful for hotels and restaurants, and the Disney website gives a lot of information, but the best place to ask any questions is the Trip Advisor Marne La Vallee Forum, which is the forum for Disneyland Paris. People there know DLP very well, and can answer most questions about anything to do with Disneyland Paris.It is a very friendly forum.