If you don't recommend it, the money you can earn is also very meager, and the investment is greater than the income. Couplets are consumables and seasonal. Now most couplets are printed, and ordinary people don't spend money on handwritten couplets. Even if they are willing to buy printed matter that exceeds a certain range, they will not choose. If you are willing to choose handmade couplets, there are related writers in general life, and you don't have to buy them online. However, if you can find customers, various companies and large-volume units, you can't say that there is no market at all.
If you write well, you don't have to write couplets.