How to contact seller who send me a fixed price offer

Kia Ora San,

You are correct - there is no way to contact the Seller through that Listing now - the best you can do is see if they have any other Listings for auction and send them a question about the car through one of those - if they don't have any further Listings you can save them as a favourite Seller so you are emailed whenever they create New Listings & Relists so you catch the car listing when it comes back up and ask your question then - hopefully no one else purchases the car meantime.

All the Best - Cheers.

How do you order multiple orders, for example,  I may want 20 but the system allows just 1?

Michael, you'd need to ask the seller. It is the seller that creates the listing and either sells 1 by 1 or makes it a buy now only listing where the buyer can choose the qty they want, obviously up to their stock level. Some sellers prefer to sell one at a time  even when they have many, and if people want more they have to click the relisted item to buy another. The advantage to the seller doing it like this is to increase their free listing allowance, but some buyers do not realise to do this, or don't want to do this, so they buy from other sellers that allow buyers to choose more than one.