Staying with what you can afford is always a wise idea.
Most factory campers will have an RVIA badge or sticker on them.
I have seen forgeries though. Basically if it’s a cargo van, it IS NOT a factory camper. Generally a factory camper will have many opening windows, a 3-way fridge, and a legitimate furnace with a thermostat, and usually a shore power hookup. Not all factory campers come with a bathroom, but I highly recommend them.
Practically no factory campers come with solar, and it is best avoided. Factory campers are made to strict safety standards, but there is no safety or quality control on DIY ones. I also try to avoid any that the owner has made modifications to, because once again you’re rolling the dice aas to the quality of those modifications. Many DIY campers or mods have been known to blow up or burn to the ground.
When it comes time to resell it, any owner mods severely hurt the resale value. Generally speaking, DIY campers are worth only what the van itself is worth, and any money put into converting it will be lost. I lost just over $30k within a year on one I built, and it was actually higher quality than factory campers, but it was a cargo van, and campers want windows.
My best advice is to stick to older factory campers, ones that are already fully depreciated. I have never lost money on a fully depreciated factory camper. I’ve put 200k+ miles on some of them and still sold them for what I paid for them, and often more than what I paid for them. That is true bang for your bucks.
With much experience (Real life experience, not Youtube/Instagram type experience!), it is possible to build a very comfortable camper van on a budget. My current van was originally a Travco camper van, but people online convinced the owner to strip it and start over. After stripping their $10k+ beautiful camper van they realized it was a horrible mistake and they were in over their heads. I bought it stripped for $700 and spent ~$300ish converting it back into a simple camper. I did it quick and cheap, planning on making it nicer later. Now, 11 years later, I am still living happily and comfortably in my original quick and cheap no-build “build”. My $700, 1973 Dodge camper van is now approaching 500k trouble free miles on it’s original engine & transmission, with nothing more than typical maintenance ever needed.
"Smiles are contagious, pass them on!" ~ Van_Dweller