I don’t think it is a case simony, which concerns mostly serious offences, ranging from buying and selling relics, church property improperly, bishoprics (or any church office or position) and so on.
This is what I found on the sale, it’s a summary I think: "This item has been added to your guest watch list in My eBay.
… This Rosary was obtained from Father
James Blynt, a very respected collector and dealer in Rosaries touched
… Papal Rosary Touched & Blessed by Pope John Paul II - eBay … - cgi.ebay.com ] "
Knowing that a pope has blessed an item can be a strong incentive to buy a rosary. Not so long ago in the Catholic Weekly (Australia) there was a big advertisement run to support seminarians (legitimately) in Africa by giving a donation of, say, a minimum of $19.00. For this you get a rosary blessed by Pope Benedict XVI (the blessing would have been a special arrangement with the Pope for the African missions I suppose or done during one of his audiences). $19.00 is about average for the price of rosary beads. I was tempted to make a donation to obtain one of those rosaries because I also collect rosaries (modest collector). So, even in such an arrangement to donate money for Church purposes there was the incentive of obtaining a rosary blessed by a pope.
Second hand rosaries are bought and sold all over the world. I can’t see that a blessing would be lifted from a rosary just because it was sold, which is the only way such beads can survive unless gifted or inherited. If it was sold and
priced for the Pope’s blessing alone, that might be a minor case of simony.
Unfortunately items such as rosaries do mostly end up in the hands of people who do not believe in the Catholic faith and they will sell them for the best price they can get for them on the basis of age, precious material or even association (in this case a Pope’s blessing). You have a certificate, is it not possible that the rosary was originally sold as such to raise funds for the Church missions or whatever?
Whatever the case, I think it was a great gift from your father-in-law and if I were you I would treasure it for life. In the worst case scenario, you can know and say, ‘This rosary
was blessed/touched by Pope JP II’, you can’t erase that.
Consider too that a rosary does not need to be blessed to be used by the faithful.
But if you want to be absolutely certain about the blessing aspect, you can take the rosary to Rome or have a friend take it (its a great place for Catholic pilgrimage) and attend the weekly audience with the Pope who will bless it as part of his general blessings for such items toward the end of the audience. Then you will have a current blessing on the rosary by the present Pope and you can then consider that the rosary
was blessed by two popes.
I’m sure you will love praying on your rosary!