To illustrate, I recall one professional home inspector telling me the water heater was working fine but was nearing the end of its useful life. He was right. About a month after I bought that house, the water heater sprung a major leak. However, don't expect home inspectors to know everything. If an item could be defective but the inspector isn't certain, their written report will often recommend an inspection by an expert.
Some home inspectors are really repairmen in disguise looking for work.
Occasionally, an inspector will be instructed by the buyer to create home defects, which the buyer will then use to renegotiate the purchase price to drive it down. This happened to me a few years ago with a house I was selling. The buyer's home inspector, a retired contractor, said the furnace was defective and should be replaced. Since I hired another professional inspector at the time of listing the house for sale with a Realtor, I didn't agree because my inspector reported the furnace was in good condition. To satisfy my buyer, I arranged for a local gas company representative and a furnace repairman to check the furnace.