Is the furnace working?
How about the air conditioner?
Are there any plumbing leaks?
What about the roof?
Most buyers don't know much about the mechanical, electrical, and plumbing systems in a home. They wouldn't know if the house is going to fall down or not. Neither do Realtors know. Texas Real Estate Commission (TREC) licenses Home Inspectors in respect to a real estate purchase. They are not engineers (at least they are not licensed as engineers and not required to perform engineering functions), but some home inspectors are licensed professional engineers also.
An appraisal is not an inspection, and an inspection is not an appraisal. Appraisals are for lenders. Inspections are for buyers, except the WDI. Inspectors don't do many things but are required to do a specific minimum number of tasks according to TREC standards. Many inspectors do much more than the minimum, and in particular try to get a potential buyer to understand the inspector's findings. Included in their report, providing they can access the things being inspected are:
Because inspectors are not experts in all specific areas, they may recommend having a qualified HVAC technician inspect the heat exchanger and other components of a system, including Freon levels.
They may also suggest having termite or other pest inspections. Many home inspectors are also WDI (wood-destroying insect) inspectors and can give a termite report usually for additional charge. Many lenders require a clear WDI inspection.
Wells can be tested by some inspectors, but a safety inspection would normally be handled by someone else.
Leaks under a foundation slab would not be handled by a home inspector because it is not accessible. A plumber can test for plumbing leaks in a separate test. Typically these tests are suggested to discover the cause of heaving under the slab.
Analyzing a problem is not the responsibility of the inspector, but often their expertise will suggest a possible cause to be investigated. A sprinkler system with one head not coming up could be a broken control wire or a defective panel, for instance.
A good inspector will not only explain his findings to a potential buyer, but also provide a written report with photos showing potential issues.