With Black Friday imminent and Cyber Monday on the horizon, this "interesting psak" is timely.

Someone asked Rav Shabtai Yagel, rav of Bnei Hayeshivos community in Ranana, specifically about Black Friday and Cyber Monday but also relevant year round in general, if purchasing goods via the Internet, especially from abroad, is a problem is hurting the livelihood of other Jews. Traditional storekeepers are little by little losing their market and customers and their sales numbers continue to decline. What right do we have to hurt their parnasa like this?

Rav Yagel responded that the issue of "יורד לאומנותו של חבירו" - harming someone else's trade - is an issue of opening a store near someone else's similar store and by opening yours in the proximity of the other person's you will harm his business. There are serious issues involved to be discussed, such as is the storeowner a local or from somewhere else, will his sales go down or will he have to close the store, and more.

The case in the question presented is different. Buying goods online has nothing to do with the issue of harming someone else's business. The way of the world is that one item replaces the previous one. One method of commerce comes along and replaces the previous one. Merchants need to adapt to new realities. For example, electric bicycles are harming the sales of traditional bicycles. Should one not buy the new electric bicycle in order to protect the old bicycle market? Obviously not.

With more and more commerce taking place online instead of in traditional brick and mortar stores, merchants need to adjust, as this is the way of the world.

However, Rav Yagel adds, there might still be an issue with giving preference to Jewish merchants over non-Jewish merchants. There is definitely a halachic preference to doing so, but that does not apply when either the non-Jew is selling it at a significantly cheaper price or if the quality-level is very different. As well, if it causes you more difficulty, you do not need to go to the Jewish shopkeeper - buying online is much easier than going to a store across town. And, many poskim say that this preference, even when it applies, is not halachic but a good thing to do.

It is good and honorable to help a Jew, a religiously observant Jew, earn a living.
source: Srugim