[Applies to charm] They charm him into writing the letter
[Applies to influence] They influence him to write the letter
[Applies to tempt] They tempt him to write the letter
Adjective
S: (adj) charming (pleasing or delighting) "endowed with charming manners"; "a charming little cottage"; "a charming personality"
S: (adj) charming, magic, magical, sorcerous, witching, wizard, wizardly (possessing or using or characteristic of or appropriate to supernatural powers) "charming incantations"; "magic signs that protect against adverse influence"; "a magical spell"; "'tis now the very witching time of night"- Shakespeare; "wizard wands"; "wizardly powers"