Assuming you are speaking of residential property, like a single family home, the value is typically determined by comps or comparables. This would be the value other similar homes have sold for locally. If a home on the same street with the same number of bedrooms and bathrooms in similar condition sold for 150k, then it is safe to say you are in that ballpark. Take that same scenario but say the 150k home was a 2/2 but the home you are looking at is a 3/2, then the 3/2 would, of course, be worth more. The same goes for bigger lots, garages, condition, etc. You can look on realtor.com, zillow, etc and find comparables for properties in your area.
Home inspectors will give you insight into things that normally can devalue a home. Such as a termite problem, electrical issues, bad roof, etc. They are important, but they also are not appraisers.
If you have an appraisal done usually there is an appraisal contingency so you have an out from the contract if it comes in under market value.
Lastly, no one person can tell you what a home is worth, especially if it is a personal residence. If it is your dream home or meets a specific need, it may be worth a lot more to you than it is to someone else.
