Knowing what your end product is worth, and what it will cost to get it to that value, is all it takes.
Those numbers are easy to verify. They aren't a secret or take any kind of special skill.
Professionals can tell the difference between those who have put in the work to know what they are talking about, and those who havent'.
So, find a property and start to work it out as if you are in control. Look at the properties around it that have recently sold that are comparable in size and finishes. (same beds/baths/sqft)
If you need to make upgrades you can use google to find cost or hire a pro to give you the numbers you need (not the same as "getting estimates". A pro provides actual cost, not "estimates".)
Even if you get all the facts, and its a good deal, and you are still too scared to "pull the trigger" then you can "wholesale" that property. Make a few grand and then go find another until you feel you know enough to take the next step.
Its not easy, its not fast. But thats why there is real money in it. Control yourself, control the information you take as fact, and control the amount of return you get on your investment (of time).