Generally I only buy electrical fixtures (lights, fans, etc.) from a reputable seller out of concern for fire risks, but if AFCI breakers and GFCI receptacles are installed, would that eliminate any potential for fires / dangerous issues if there was either a faulty fixture or wiring in the house?
Do AFCI and GFCI protect against cheap equipment?
Not really. A GFCI will limit a shock and an AFCI will limit arcing. There are many other things that can happen with non listed equipment. I specifically look for a UL listing or TUV true verification that the devices are safe to use. Some JUNK may not arc or have ground faults but overheat and start a fire.
So NO even the combination AFCI + GFCI devices can not protect for these cases where no arcing or ground faults happen. Poorly chosen components that over heat and start fires can still happen.
What’s worse is some devices cause nuisance tripping, no faults, new replacement more tripping the owner removes the AFCI and the device ends up causing a small fire (usually contained in the junction box).
If the cheap equipment is so cheap, that you experience a live-neutral shock, you will die, and neither the GFCI/AFCI will trip, because killing you became the load. You'll be long dead before the lowest rated breakers will trip from shocking you.
AFCI/GFCI do not cover all possible source of danger. It covers some of it and can make things safer, but electricity will still kill you. Don't do stupid things and think AFCI/GFCI can compensate for garbage electronics.
At the very least, you need to comply with NEC 110.2 (it's on the first page) which says you must use approved equipment. In practice that means listed by an NRTL such as UL, CSA, ETL, BSI, TUV and the like, this being independent lab testing to positively confirm the appliance complies with the relevant UL White Book standards so it won't kill you. And then, continued surveillance of factory output to assure the factory doesn't bait-and-switch.
*It sounds like what you're saying is, "Is it OK to use the cheap Cheese junk I see on AliExpress, Amazon, eBay, Banggood, DealExtreme and wish.com" the vast majority of which are not listed.
Right off the top of my head, here's a fatal blunder: As you know, any random plastic will burn like a freak and produce toxic smoke; very commonly in house fires, the toxic smoke overcomes you - it doesn't need to kill you clinically dead, just incapacitate you and the smoke/fire does the rest. They must be made out of the right plastics (expensive) to NOT do that. The right plastics cost money.
That's an immediate example of something AFCI and GFCI won't protect against.
That cheapo stuff online is all about cutting every possible corner on costs, so they dispense with both proper materials and independent lab testing. Since most consumers expect an NRTL mark to be there, they just stick a CE, CCC, FCC or RoHS mark on there, none of which are NRTLs but you don't know that. They either don't relate to device safety, or are voluntary self-certifications that are unenforced outside certain jurisdictions, so no consequence for faking them.