I been in NAV for about 7 years & when i first started I also thought NAV was not good, but when I started exploring and got my expertise in it and i have developed 100’s of solutions, new developments in NAV.
NAV is goodddddd. MS has always come up with new thing in NAV like the web service, RTC, search in reports, direct tele call from RTC page.
As for victor, there are business rules for every software (i.e. Financial, ERP, SAP, Tally or even excel application developed for Small Industries).
And if you do not know which NAV table are going to affect then would be good to ask a end user of the validations rather to just start coding without knowing the business rules, cause the data what you are inserting will effect the whole busines financial data.