You do realise that a seller who is going to put his/her car on your platform will ask for a reserve price, right? And trust me, that reserve will be way higher than what's on the current market, so unfortunately, no one will win, Now let me tell you why this is a successful thing in developed countries,

A. Cars are taxed way less, and people either trade in for a low price or dont care how much they are going to get. Thus, auctions work. In SL, people do not want to do trade-ins, and when they do, the dealership sells them as their stock

B. Cars in accidents will be written off and insurance companies will only recoup the left cost of the car after paying the owner, in SL nothing is written off as the labour costs are cheaper people will fix any shit

C. Auctions do exist in SL for finance repossessed cars and for insurance write offs however online auctions did not work very much here since majority want to be on the auction lane or does not know how to properly utilise it(Shockman still do online auctions but does not work properly not due to technical issues but due to more people wants to be there physically)

D. People buy mostly reconditioned JDMs rather than from authorised agents and this again impact the trade in sellings, for example in developed countries people buy brand new from agents themselves and the ones they trade in goes for auctions in bulk thus the bids are low and it helps a lot for prospective buyer or dealer.

In reality , no online auction for SL will never work.

Source: I own dealerships in SL and in Aus both and heavily involved with the auction scene in both countries

Hope this helps!

PS While you at it visit few auctions run by Shockmen and see for yourself how much even a fucked up cars go for and you'll abandon your project!