Reason being is if there is something that was missed in your initial inspection that another contractor found, you can go back to the realtor and demand them to be fixed. Especially for new builds.

However you only have a small window for this, because if you wait too long the realtor and or contractors can say it was you and it's not their responsibility.

Also you should always get multiple bids from several contractors. If someone is going to do the job at a really low price, that means that contractor will cut corners, and do more harm than good. If someone is giving you an astronomical price that is completely unreasonable that means the contractor doesn't want the job.

There is also this other "tactic" that construction companies know very well. That is if the company is trying to give you a deal, you as a customer are going to nitpick every little thing. Flip side, if they mark it up the customer will always believe it's the best job that was ever done.

Source: my step father owned a large legit construction company, that I worked for, and my bio father owned a small shady construction company, that I also worked for.