In general, I prefer buying online, all else being equal. As previous posters have said, a few clicks is a lot easier than driving to a dealer.
I do, however, think the "which types of parts to carry online" question needs some thought. It seems to me that there are several broad categories of parts (obviously with some overlap):
- Comsumable parts. Filters, belts, etc. These parts work well online, since the need for them is usually known in advance for scheduled maintenance, and owners don't mind buying a few extra, since they will use them eventually. The problem here is competition for commodity parts. What can you offer than no other online parts service offer? And, as is seen here on TBN, a lot of these types of parts have local (NAPA, Wix, etc) equivalents that are cheaper/just as easy to obtain as the manufacturer's part. Maybe offering the equivalents online (with a good cross-reference system) would be the ticket?
- Emergency repair parts. Parts that break (as opposed to wear out) infrequently, but when they do, the tractor is out of commission until the new part is obtained. The problem with these parts is that owners won't want to stock up on these parts, and (assuming a decent inventory) a dealer can get the parts to the owner immediately, whereas an online service will force the owner to wait at least overnight. Price is not a major advantage here, since owners will likely pay a (slight) premium to get the tractor running again within hours instead of days.
- Major overhaul/restoration parts. These parts could work well online, since the tractor is already torn apart, likely for "known ahead of time" service.
So, I think it's worth thinking about what types of parts you would offer, and what you can offer regarding those parts that other online services (including the manufacturers') cannot (or don't) offer.
As I mentioned above, it might be worth considering offering aftermarket consumables with an easy-to-use cross-reference system. There have been an awful lot of posts about what Wix filter matches a Kubota <fill in the blank>. I don't know if the tractor brands you carry "allow" you to do this, however.
Anyway, food for thought.
Rick