Not knowing what they can afford before making an offer.
The best way to avoid this is to get pre-approved for a mortgage so you know exactly how much you can afford. Usually pre-approvals are free.
Not knowing who the agent represents.
Unless an agent is working as your buyer representative, they represent the seller. Many people don't realize this.
Choosing the wrong mortgage.
A bad choice can cost you thousands in taxes and interest. You should consult a mortgage agent and ask them to spell out the total cost of borrowing for each option. Also important to know the penalties you have to pay if you break the mortgage early. This will enable you to make an informed decision that lines up with your purchase goals.
Not finding problems with the home before buying it.
You should always have a certified home inspector look at the home before buying it, otherwise you could be looking at huge repair costs later on.
Not understanding how their credit can impact their ability to purchase or refinance a home.
Your credit score can mean the difference between qualifying or being rejected by a lender. If you have a low credit score, it does not have to be forever! Consult a mortgage agent/specialist to find out how you can improve your credit score.