Much as you might want to go above and beyond and find a way to help every buyer or seller that comes your way, there’s no avoiding a certain fact as a Realtor: There are some kinds of clients that are just flat-out toxic. Here are a few to watch out for and some tips on what to do if you encounter them.

The Client Who Knows Best

Clients like this come into the transaction mistakenly believing they know enough about the real estate market to distrust your expertise, disregard your advice and generally proceed as they see fit, a course of action that will often lead them into trouble. They may want to set their home’s price regardless of its actual market value or might attempt to bid so extremely far below a seller’s price as to be unrealistic. Whether a buyer or a seller, they can wind up stranded in the market.

Fortunately, with some patience and careful education, it can be possible to bring this kind of client around. Giving them stats and some honest talk about pricing, and including them as much as possible in the process so they can see how it actually works as opposed to their preconceptions, can make the difference. Some opportunities might be lost along the way, but most of the time it’s still a salvageable situation.

The Overdemanding Client

This kind of client doesn’t necessarily have unreasonable expectations as far as pricing or the process of negotiation goes. Nevertheless, nice and reasonable as they can at first seem, they quickly develop a pattern of gratuitous demands on your time and energy. They will ask for irrelevant research out of simple “curiosity,” will regard you as being on call to hear out every passing whim or desire at all hours of the day and may effectively seem to expect you to provide an unlimited amount of labor for free.

The good news is that this kind of initially toxic client can be educated. It’s good practice to try to go above and beyond, but if the expectation of doing so goes beyond reason, it then becomes necessary to set boundaries and train them to understand your working process. Hold firm on those boundaries, politely direct them to supplementary research sources if they want more information and keep them focused on closing the deal. Even if there’s some initial resistance, you will often find them coming around.

The Relentless Pessimist Client

This kind of client often nurses unreasonable expectations that they can’t admit to — such as buyers who expect homes at impossible prices in unlikely areas of the market — and, as a result of those inevitably disappointed preconceptions, become relentlessly negative and resistant to advice or consultation. They may stay at it for a long time, at considerable expense of their time and especially yours, until they finally decide it isn’t worth the effort.

The relentlessly pessimistic client is best simply avoided, if you can spot them in time. It’s always a good idea to identify unreasonable expectations early and try to hold an expectations-setting conversation where you can lay out the realities of the market to them. Get a clear picture of what they’re looking for; lay out the practical drawbacks of overexpectation. If their preconceptions seem impossible to satisfy right from the word “go,” there’s nothing wrong with simply telling them in the nicest possible way that their goal just can’t be achieved. In the long run, it will spare both of you plenty of hassle.