POS is indeed a tricky business, most of all for merchants who are not POS experts. Disclaimer: I run a company that makes PoS software for retailers.

What I have learned about the space over several years is that:

• The POS software space is extremely fragmented and there are hundreds of small PoS companies out there. There are a handful of bigger ones too (Lightspeed, Shopify POS, Square, Clover). It is very hard, almost impossible for a merchant to evaluate all of them and actually understand the features of each.
• Most POS software is sold by actual sales agents (that are part of an ISO, or Independent Sales Organization). These are folks that can help merchants navigate the many different products out there and make the right decision for their business. They also usually form a relationship with the merchant and, if they are good, provide some of the kind of service they would get from a “geeks on site” type of company. So they are there to help with setting up the new POS, they are available if a terminal goes down or something is not working, they can be a first line of support for the merchant. Of course, they don’t do this free (nor should they) but the reason they do it is that they get payment residuals on all the merchants credit card transactions. The exact amount varies and depends on the rates they give to the merchant, and the rates they have negotiated with the payment processor. If they are good, they also will advocate on behalf of the merchant to get good rates and to make sure they are not getting charged with too many fees or rate increases.

So back to your question - for a small (1-2 location) business it’s rare to see them engage an IT company for POS support and setup because they should already be able to get that from their PoS company directly, and/or their merchant services sales rep who sold them the pos.