It can be, if you check the right things. You cannot test the sound before paying, so the seller and the product page matter more than they would in a shop.
A trustworthy online stethoscope listing explains how the device works, not just how it looks. It names the battery and connection details for digital models, and it states the warranty and return terms. If a page has only photos and slogans, ask questions first or look elsewhere.
Also ask a senior colleague or teacher what they use and why. Their daily experience is more useful than an advertisement.