A few remarks from me, basing upon my personal experience.

There are two main types of the customers in online transactions:
- "the refurbishers", who want to get the truck to resell it.
- the endusers, who wants to buy the truck and work with it.

The first want to buy possibly cheapest truck, make the repairs, paintings etc. and sell it as "nearly new"
They don't need the warranty. They need the exact specification, a RELIABLE and possibly detailed technical info about the condition of the truck, the REAL workinghours, etc to enable them to presume the refurbishment costs and the possible margin. Other words, they need the information which sometimes definitely exceeds the endusers requirements.

The enduser, from the other hand, expects the basic (but exact) specification, information about the overall condition of the truck, warranty conditions (the longer, the better), service avalability, location and costs, many nice pictures, the price (I personally hate the tabs "call to get the price" very often visible on the dealers pages), delivery time, informations about the attached documentation (operators manual, certificates, spare parts catalogue etc.).
Very good impression makes the "references" page, where the letters with the positive opinions from the previous customers are visible.
Of course, for the endusers, the "quality levels" markings can be used, like 3,4, or 5 stars or "basic", "premium", "awesome" ;-) but they must be clearly and with all the details defined on dealers page.

To be frank - I don't believe in international or national codes of ethics in sales, because very often the people have different recognition of the ethics in bussiness.
At end of the day, what really counts is the the dealers reliability, clear information and simple honesty of the dealer.
On our (average in size) market in Poland, the information about cheating suppliers is spread very quickly.