Don't set it so high that you'd never pay it, but not so low that the buying club refuses the transfer entirely.
Adding this clause usually forces you to accept a lower upfront transfer price because the buying club is taking on the risk of losing the player. buy back clause fm12
Even if the club accepts the bid, the player can still reject the contract if they feel they've outgrown your club or dislike you. Don't set it so high that you'd never
Use it on 18-21 year olds who aren't quite ready for your first team but have high potential. your £5M clause becomes useless
If the player flops and his value drops to £1M, your £5M clause becomes useless; you’re better off just bidding normally. Best Use Cases