You are likely to need a suitably sized vehicle for collecting new stock, delivering items to customers and auction houses and so on. This could be a large estate car or perhaps a van. You will need to make sure that your vehicle is capable of transporting antiques safely and securely without damaging them.
The older the vehicle the less it will cost to buy, but very old vehicles may not be economical to run and may project the wrong image for your business. An alternative to purchasing a new or nearly new vehicle outright would be to lease one.
Consider whether you will need to fit a roof-rack for transporting very large (but probably not very high value) items. A trailer might also be useful.
Make sure that your motor insurance company knows that the vehicle will be driven for business purposes, possibly by several different drivers.
If appropriate to your type of business, you could consider getting your vehicle sign written. A smart, sign written vehicle can be an excellent advertisement for the business.