I think the only risk in accepting crypto as a payment method is the volatility but if you would convert it into Fiat right away then there wouldn't be a problem.
But you should also consider the transaction fee's and the delay of transaction.
I think you shouldn't really worry about it since it is just going to be an option on your online store you could also add more option for them.
He can accept other crypto like XRP where volatility and tx fee is not much of a prob. Some consumers will be hesitant to use bitcoin because of the relatively expensive fee that they need to pay on top of the price of the goods. But bitcoin is a start, to see if some of his clients will try paying btc. And if they ask for alternatives, then XRP is a good one or maybe doge. Anyway, he can always exchange these 2 alts to a lot of exchanges if he wants to.