Good question! Integration is one of those incredibly important points that usually isn't "exciting" enough to get a lot of attention. But it's actually a huge factor in our business.
We have 3 ways to integrate with stores:
1. Plugin for supported platforms: Shopify, Magento and AbanteCart for now. This method is definitely the simplest one - usually not much more than a one click install.
2. API calls: We open APIs for reporting information (which user showed interest in which product) and decision (which items should I show this user on this page). This will usually result in a very small amount of lines of code inserted at various places in the store's codebase. It's also great because it really is quite independent of any specifics of the store's implementation.
3. Custom JS: This will result in a small but not negligible amount of work on our side which will result in the store needing to insert a single line of JS into their template and everything will work. We'll generally only do this with larger stores where we can justify the development on our end.
In any case, we don't want the store owner to have to do any meaningful amount of work in order for our product to run.
If I have a custom site, what are the chances you could work with it without expensive customization?