I like primary sources. I use public record. Here, for deeds and mortgages and anything recorded, we can read the entire document, unlike some states that only pass on a very redacted title abstract (in some older cases, I am turning the hand-inked page). I do use MLS and try to corroborate data, especially the often subjective stuff.
How many times on here have I criticized Realist because when I check it, it is often wrong? Other appraisers have no such qualms. Either. in their markets, their records are more centralized and so it is easier for aggregators like Realist to get right, or they figure good enough because using it is accepted. No one who is happy with it on this forum has ever replied that they checked it for accuracy--even once.
I read the zoning regs every time, and it is work here because every town makes its own regs.
When appraisal software automatically offered flood map citations, I disclaimed errors from that source. Never heard of any, so I do not go check that.
Third-party: MLS, fsbo sites, realist while eyerolling, flood mapping.
Primary sources from the authorities who compile or maintain the records for the public: land records, zoning regulations, assessor records and sketches, building office files on the property (I often compare data from MLS comps to these records), parcel mapping by the local authority
Am I working harder and taking more time than your rostered folk? Probably so, but your company and its peers have made risk decisions on what is acceptable. And some appraisers accept sources I would not because those fit their risk tolerance. For hybrids, I would have a hard time accepting data from someone not picked by me, or whose work had never been seen by me.
This is a basic list off the top of my head because now I am leaving to inspect because I agreed to meet an owner after they and their tenants got out of work. Last property of his I inspected, I got a lot of information from this investor which went into my files for appraising multi's in this specific market. I don't think your inspector would have asked those sort in-depth questions, nor would it have been passed onto me as the signing appraiser.