I supplied software to quarrying and waste management companies for over 30 years without a single problem, or error. I always resisted requests to directly connect into the accounts system my customers used.
In Britain they were generally SAGE and PEGASUS, plus one or two others. I didn't offer QuickBooks because it was aimed at smaller companies. One man and his dog, small builders, or car dealers. None of which I would want to deal with anyway. I would import data, usually the customer list from SAGE and export invoices in a CSV for SAGE to import. As so often is the case inexperienced book keepers used the accounting systems on a daily basis to enter data and the possibility for errors I thought was high.
I would create a file that SAGE would import and update the sales and nominal ledgers. I would also export new customers that didn't already exist in SAGE. After that, SAGE would then validate all data before importing, which meant the two systems were independent. If I linked directly into SAGE and something went wrong, SAGE I presumed would stonewall, whilst my client will be going barmy and I would end up with the bill to put it right. The import protected me from that. You just need a system to prevent, or correct a duplicate import. SAGE will happily import duplicate data!
The QuickBooks import/export file I understand to be basically standard OFX files. The same as most banks use for your exporting accounts data. So fairly easy to create your OFX import/export text file routines. If you are new to OFX, don't think that it is a series of records, as a RandomAccess text file. It is a Sequential File with one record.( I did have a discussion in the forum about that but the other poster(s) somehow didn't see that, despite my reiteration)
In summary I would never link directly into any accounting software. Some do and good luck to them. I'll present valid data to the accounting system and the accounting system will only import and update its ledgers with what it concludes to be valid data. Therefore providing me with confirmation that my export file is correct in every way. But always your choice of course, I'm not saying you shouldn't.