One of my first jobs was writing integration software for different accounting packages, and BOY OH BOY are you correct.
Many (most) packages have an API, but transferring data in and out requires deep knowledge of systems, their special pricing rules, their tax rounding rules (which is also different for every country) and many many other things, it was difficult enough for someone with years of experience in this domain to get right, the chances of even a senior developer doing this properly without field experience is zero.
Many (most) packages have an API, but transferring data in and out requires deep knowledge of systems, their special pricing rules, their tax rounding rules (which is also different for every country) and many many other things, it was difficult enough for someone with years of experience in this domain to get right, the chances of even a senior developer doing this properly without field experience is zero.