How do you get decent money for your players?

Ok this has been bugging me for ages, i constantly see the AI buying and selling players between each other for large transfer fee's i.e 50+ million, yet when it comes to me trying to sell players, they only ever offer the market value or less. Example i'm in the year 2026 i have this midfielder who's 28 has a PA of 185 and his CA is 184, he won the wolds best player for the last 3 seasons, he's been with me for 10 years and wants a new challenge so i said i'd let him go, i offered him out for his market value of 28 million, the only offer i got was a loan offer that i declined, two days later Aston Villa pay 20 million for a 30 year old player with a 156 CA. My team is loaded with talent yet the highest transfer fee i ever recieved was 22 million, even though i tried to get more, that was as much as i could get two years later Barcalona buy the player i sold for 22 million for 55 million. It seems totally unbalanced in favour of the AI.