无事献殷勤，非奸即盗
wú​shì​xiàn​yīn​qín​fēi​jiān​jí​dào

beware of Greeks bearing gifts

无事献殷勤，非奸即盗 無事獻殷勤，非姦即盜 wú​shì​xiàn​yīn​qín​fēi​jiān​jí​dào
beware of Greeks bearing gifts
one who is unaccountably solicitous is likely hiding evil intentions; literally, 'one who offers favors for no reason is either up to no good or trying to steal something'