Why would you have any concerns as it's not even run in if those kms are right, some buy a new bike because it looks great to find out after it's not the bike for them, when I brought my new 2016 Thruxton S in 2018 (new old stock) one of my riding mate brought a new 2017 Street cup the same week, after 2 weeks and a few rides together he knew the Street cup wasn't the right bike for him and he traded it in on the same model Thruxton as mine, he was lucky the dealership he brought the SC from gave him a good deal on the new Thruxton S so he didn't lose much money from the deal just had to pay the extra for the 1200.
Do you know the reason it has only 500km on it and the reason the owner didn't ride it, if it's been stored right fuel drained out it should be fine after a full service and fresh fuel.