If you're a small club and are not winning much in the way of trophies, then of course you would be forced to sell your best players eventually. If you somehow manage to keep player salaries relatively low while winning trophies then you would be selling players less often.
I'd started with the default ML team with one of the fake teams and put myself in the Championship so as to avoid any extra money or fans coming out of nowhere. I'm in my second season and so far I'm just trying to update my facilities before I think about spending too much on players. There's hardly any money to be made at the moment (£80,000 for winning home games ffs) but I think the club is going in the right direction (not having trouble paying my players and staff at all yet), and within 2 or 3 seasons I think I'll be challenging for the Premier League title if I continue like this.