Which mechanic diagnosis do I trust when they completely disagree?

“Had an hvac tech out to look at my AC, and he told me to stop buying expensive MERV 13 filters because they restrict airflow, and to start buying cheap filters and spray them with cooking spray to catch hair. That sounds like the dumbest thing I've ever heard, but I'm coming here to see what the council thinks.”source ↗

“Does the used tranny oil in the pics and vids linked look wrong for my car? I've been driving it for more than a year (full summer/winter cycle) and haven't noticed anything.”source ↗

“If it is, how to approach the previous mechanic to confirm and take some responsibility (maybe drain/fill until the bad fluid is flushed?)”source ↗

“One shop is telling me it has completely failed, and the shop that replaced it is telling me it's fine. Who should I trust?”source ↗

“Thank you everyone, they keep swearing up and down that I'm wrong and throwing a fuss about reversing what they did.”source ↗

“I went to autozone and they did their free diagnostic look. It showed up that I need a new engine water pump. I had an independent mechanic check it out and he said there is a leak and it’s draining my fluids and the head gasket needs to be replaced, it’s not a water pump issue.”source ↗

“My question is, can a head gasket cause water pump issues? This is a big difference of $1000, to close to $5000 and I don’t want to proceed unless I’m absolutely sure.”source ↗

“The last image is an influx of them from the inside of our patio sliding door. We notified our apartment complex ASAP, and of course, we have to use the company they have a contract with.”source ↗

“and the sweetest lady said they weren’t bed bugs. she even looked at them under the a microscope to confirm, and identified them as a grain beetle. on the contrary, I sent these images to another company, and they said yes, they are indeed bed bugs.”source ↗

“The apartment complex’s company is coming out today to inspect, but I’m just really confused.”source ↗

“Now I’m confused because the diagnoses are different.”source ↗

“My biggest confusion is why Chevy identified the valve covers but not the oil pan/rear main/transmission pan, while the independent shop identified those but didn’t originally list the valve covers.”source ↗

“Would you trust one diagnosis more than the other?”source ↗

“I genuinely dont know what im looking for or anything about cars. If I could I would!!”source ↗

“The dealership said my left front control arm bushing is cracked... when I took it to Firestone, they said that’s just a normal crack.”source ↗

“Am I crazy? I've used the cabin heater for a while and it always worked to stop overheating, but now I got 3 different mechanics telling me that's impossible.”source ↗