Lol, what the fuck? He's been statistically our best attacker for two seasons, we're a club trying to make forward progress and compete for top honours… mostly the CL (so Europe's best sides) and in our league (which is arguably the most competitive league, rather than other leagues that some might argue are just a glorified SPL). It's not a mystery that a club that's made good progress over two seasons would want to keep their best performers over those seasons. I'd only entertain an offer that makes PSG's offer for Neymar look miniscule in comparison... so an absolutely obscene amount of money.
The reasoning that you'd sell him for being selfish, no offense, made my eyes roll around in my head roll around so quickly that I had to take several seconds to rub my eyes and regain focus so I could type this. You know who else was selfish? Thierry Henry, who a lot of players consider the best attacker in history of the league. If an Arsenal fan had insisted to me that Henry could be replaced if he'd hypothetically scored 40 odd goals in his first season and another 20 something in his second season (I'm using hypothetical stats that match Salah's to illustrate the comparison) after his first two years at Arsenal, I'd have laughed in his fucking face til I was out of breath and crying.
Here we've got a player that in his time with us has given us the best form of his career, suited to our system brilliantly and working very effectively with our current squad consistently for 2 seasons. This isn't like Coutinho being brilliant half the time and average the other half the time, it's not even close to that (although giving credit to Coutinho, he was consistently excellent... after we'd established Mane, Firmino, and... Salah... as our front 3, just prior to selling him). This is a player that since we've signed him has raised the level of the other two attackers that play alongside him. Just look at last year's CL final to demonstrate his impact, we were playing really well while he was on - when he went off we became absolutely toothless.
He's a fucking talisman at this point. The only way it's acceptable to sell him is if it's a truly staggering amount of money. And even then, it's only worth selling him for that staggering amount of money until we've got a replacement either signed up or in place and we have a plan for how that staggering amount of money will be spent (because after you receive a staggering amount of money and you try to sign other players, you may find that clubs are now asking for a cut of that staggering amount of money). And even then, there's no guarantee Mystery Player X coming into replace Salah will fit the system as well as he does, or even half as well as he does, or if they'll even adapt well to the league.
The club should be doing everything it can to keep our front 3 with the club during their primes. Even if we manage to sign a better winger for our system (which I don't think would be that easy), I'd like us to keep our quality players around as depth because we're competing against clubs like Slave Trader FC and their unlimited wealth.
tl;dr - Lol, what the fuck?