The more payment methods, the better. Although, I don't think that anyone is going to buy with bitcoin currently. You realize that he/she has to pay product's price + ~$7 in order to get the transaction quickly confirmed. If the fee was much lower I would suggest adding it.
Well, it's not like that. The most commonly used payment method is enough in any existing store. But if it's an international store like he has a lot of customers from different countries then he/she consider adding different payment methods to receive money. I honestly like platforms that have different payment platforms, it makes my life easier when buying stuff online but I will not choose a payment method that has higher fees.
There are always risks like what steam does, they remove the bitcoin payment method since the volatility and high fees of cryptocurrency affects their business.
https://www.theverge.com/2017/12/6/16743220/valve-steam-bitcoin-game-store-payment-method-crypto-volatility