It's important to be aware of anything that may be unduly influencing our evaluations.
As an example Dr. Robert Cialdini warns of such a situation by pointing to the unethical comparisons that certain realtors will employ when attempting to influence purchasers. By first driving through a largely unattractive area of town, viewing properties that are wholly unsuitable, potential homeowners come to see as even more attractive properties that would otherwise be just acceptable if they had experienced them in isolation. As buyers, therefore it becomes important to be fully aware of the environmental situations and cues that may be unduly influencing our evaluations.
Still curious? Read Cialdini's book Influence: Science and Practice.