Wǎngshàng de jiǎnféi fāngfǎ duōrú-niúmáo, dàn yǒuxiào de méi jǐ ge.
There are countless weight-loss methods online, but very few that actually work.
Tips
history
From the 《北史·文苑列传序》 (Tang-era history of the Northern Dynasties): 'students are as many as the hairs of an ox, those who succeed are as rare as a unicorn's horn'. The idiom usually carries a quiet hint of that contrast.
usage
Often slightly dismissive - 'a dime a dozen', 'lots but unremarkable'. Use it for things you want to call common to the point of being unimpressive.
