The Deed: Chicago

Real estate mogul: This is the biggest mistake house-flippers make

While it's fun to admire the final product of a successful house flip, it's also easy to forget that developing properties is complicated.

As real estate mogul Sean Conlon told CNBC Wednesday morning on Squawk Box, "Murphy's Law tends to dictate home rehabbing: If it can go wrong, it will, and it generally does."

In the same interview, Conlon, who made his millions selling real estate and now hosts CNBC's "The Deed: Chicago," shared the biggest mistake first-time property flippers make: not double-checking everything they do.

Sean Conlon of "The Deed"
Maarten de Boer/NBC | Getty Images
Sean Conlon of "The Deed"

You have to "trust, but verify," the self-made millionaire says. "There's a tendency for contractors to take advantage of people who are new to the game, quite regularly, and that is where you get burned. You really have to double-check everything anybody tells you."

Before spending money on renovations, "of course, you should have a cost estimate," Conlon says. "But better still, 'I need 50 glass hammers.' You find out after the fact that probably you didn't need any glass hammers."

This mistake goes hand-in-hand with another common mistake Conlon sees house-flippers make. "They underestimate the cost," he tells CNBC in a 2017 interview. "You can take whatever you think it's going to cost you and honestly, add a comfortable twenty to thirty percent on it. You have to hope for the best and plan for the worst."

Watch Sean Conlon in CNBC's "The Deed: Chicago," on Wednesdays 10:00 PM Eastern.

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