Asking a 25 year old who's spent all his career on an abysmally bad team for a track record of success is not what I'd imagine good GMs are doing when trying to make a good deal.
Nobody is asking anyone to do anything. Point is when you make a big purchase you have to have as many guarantees as possible. The reality is his career high is 65 points. This does not make anyone break the bank. He's spent all his years losing games which does not give you any guarantees he can successfully lead a team as the 1C, we all know winning takes more than being a good player. Your top center is expected to lead the team by example, and the guy has never sniffed at the playoffs. He doesn't even have a full 82 game season under his belt as a centerman! Remember, how good you think a player is vs what he's done to warrant a certain value are completely two different things.
The only thing Reinhart has proven that potential buyers can't downplay is that he's a top 6 player, so i would expect teams to pay accordingly. But their job is to bring up all the things he haven't done, instead of talk him up like you're doing. That's not how negotiations work. This is what Buffalo is going to try to do, not other GMs.
Reinhart's abilities have never been in doubt, at least not for those who watched him. He's been a bona-fide first liner for years. The only question was, can he play center and can he carry a line without great linemates on his own, something he has now proven he can
If you can find me a single quote by a GM outside of Buffalo saying he's confident Reinhart is a bonafide 1C i'll gladly agree with you. If not, this is your own speculation. My logic tells me 50 games playing meaningless games does not prove enough. It's a positive and something that can peak your interest, but does not make you pile up a premium price.
Oh and by the way, if you expect every GM to marathon watch Buffalo games on video you'll be disappointed. I guarantee you there are some guys who have barely seen him play. Watching Buffalo games is hardly on anyone's to do list. Most will relegate scouting to other people who will have different opinions even inside the organization.
Anyway, im not sure what type of return you want, but if you're expecting him to be a big time chip that returns close to someone like Duchene, that won't happen. There will be a lot of interest in Reinhart, but there's a BIG difference between paying 1C price and a top 6 player price. The former is very specific where you don't even have second thoughts in what you're getting and you expect that player to change the dynamic of your team, and that does not describe Reinhart.
At the end of the day negotiations are about comparables and leverages, and neither is in Buffalo's favor, at least until we know more about how many teams would actually be willing to push for this.