In general such behavior is not according to halocho and There are a few halachic issues here
The Torah forbids us from deceiving another person in business (ona’ah). Chazal explain that even if the seller doesn’t try to deceive, he may not overprice an item for an unknowing buyer. Similarly, a buyer may not pay a low price for an item which he seller doesn’t realize is really worth more.
Chazal enumerate three levels of mistaken pricing:
(1) Less than a sixth – If the item was priced at less than a sixth above its market value, the sale is valid and the buyer must forego the extra payment. For the market to work there must be room for small misevaluation, and were we to retract every small mistake it would ruin the market.
(2) A sixth – If the price was a sixth more than the market value, the sale is valid but the buyer can demand that the overpayment (ona’ah) should be returned.
(3) More than a sixth – If the buyer paid more than a sixth above the market value, the buyer may cancel the sale.
In addition, there is a prohibition called Onas devorim – Verbal Harassment
As The Torah says, “A man should not wrong his fellow.” Chazal explain that one must be sincere in social interactions just as in business, and one may not harass another person verbally or cause him any discomfort (ono’as devarim).
Here are some examples of this prohibition brought in halacha:
1. One may not call a person by a derogatory nickname. Even if the nickname is generally used in a friendly manner (e.g. height, hair color), one may not use it if his intention is to make him uncomfortable.
2. One may not mention to a person a previous lifestyle that will make him uncomfortable (e.g. before he was Torah observant).
3. One may not knowingly send a person to a supplier that doesn’t carry the sought after product, thereby causing agony to the buyer or the seller.
Chazal say that verbal harassment is even more severe than causing financial damage since he hurts the person himself (not his property) and the misdeed cannot be undone (unlike a financial loss which can be repaid). If the one who was harassed cries out to Hashem he is immediately answered.
In addition, there is the mitzvah of ahavas yisroel “don’t do to others what you wouldn’t want done to yourself”
With this in mind if one fools someone to let him test drive a vehicle, he transgress on onas devorim by causing the seller additional agony, and this definitely doesn’t fit in with ahavas -yisroel
Yet it is important find out if the seller agrees because if he does (as he might as giving the chance that maybe the fellow will buy from him) and there is much reason to believe that they will agree to give themselves a chance that maybe the buyer will stick with his product
