In my experience working at a lot of companies that have a mix of in-house and third-party solutions, management generally prefers to use off-the-shelf software because of the costs and predictability. But you have to persuade them that they are not losing any functionality and can customize and integrate. People like to think that their business is special.

I still get asked to write accounting systems. I usually say "Use Quickbooks" (or any of the many available off-the-shelf packages). Then I get told "We can't, we do X, Y, and Z that off-the-shelf systems can't handle." Digging into that I almost always (one exception in two decades) find that they aren't doing anything special, they are either doing accounting wrong (they built an idiosyncratic system for themselves) or they just didn't understand different terminology or features of Quickbooks or whatever. Perhaps ironically the question of switching accounting systems often comes up after failing an audit.

I went through this with a Salesforce adoption a couple of years ago -- "We can't use Salesforce because it can't do so-and-so that our home-grown CRM does." But it can, it just uses different terminology. So you have to understand the business domain and expect this kind of resistance and know how to overcome the objections.

If you get the CTO or IT people involved they may perceive off-the-shelf software pushed on them by management and consultants as a threat to their job at worst, or a new deployment/migration/integration nightmare at best. So prepare to deal with that. IT people will focus on risks, and they may exaggerate, but you have to have a solution for migration in and out of your software (assure them they own and have access to all of their data in some standard format like a relational database), and you need to show the customizing and integration features if those apply.

Reducing friction and risk is probably the best thing you can do. Offer a fully-functional limited or trial version. Make sure you have a turnkey setup. I once worked for an educational software company that included laserdisc players with their software because requiring a school to buy those was too much friction. Have a laptop or PC you can plug in for your potential customers to use. Every complication you can eliminate to get them using your software will smooth the process, and it shows you are customer-focused. Think about how motivated you would be if someone sent you a link to a .zip file and a Word document with out-of-date installation instructions.