Livpoo were gonna get 50m for Tourist so paying 35m on a younger, English, possible England centre-forward who is a possible iconic English football figure for the next decade, and who is white and photogenic (to appeal to Far-East fans and female fans) is probably not a net-loss position to take..
Bale is not a striker (tho he could be if he wanted to) therefore as a non-forward will not command the same value..... historically its vastly predominantly forwards that command the highest fees...
Carroll's value will not disappear overnight, so they will get most of their money back even IF he fails to continue with his 1 in 2 Prem strike-rate in a better team than he was in before...