Few things:
* Remember that your eBay seller may not ship internationally. I'd strongly recommend contacting him before bidding.
* Assume that any eBay instrument will need at least $300 in repair -- and you should budget for a full overhaul (when Steve sees this, he can provide a guesstimate of how much that'd be).
* If it's not listed in the ad, assume that the instrument doesn't come with it. In the eBay ad, for instance, I don't see a mouthpiece or a floor peg. On the Gumtree ad, I don't see a bell.
* If you don't see it, assume it's damaged. A crack or split will ruin your day.
* Overseas shipping can be very expensive. You need to check.
* Customs can be very expensive. You need to check.
I actually didn't mind the Vito basses I've played. However, I know that all the Yamaha instruments I've played are very high quality. I've just not played a Yamaha bass. With the eBay ad for the Yamaha, tho, note that it's not a Buy it Now auction. The final price on the horn could be really, really high. I'd actually almost rather get one of the
Selmer USA plastic bass clarinets for $329 (provided the horns have no other problems) and buy a good overhaul. That
$500 Jean Cartier bass on eBay also looks pretty nice to me, but I have no experience with Jean Cartier bass clarinets ("Jean Cartier" was the name of a Dolnet saxophone stencil).
Do stay away from the horns that are made in China. They're not known for high quality.
While I was moderately insane and owned my own bari sax by age 16, I didn't know of anyone around my age that owned anything more expensive than a tenor sax. Additionally, I had made the decision to go to college for music by that time. I therefore ask, "What will she do with the bass clarinet?" If it's, "Just play through high school," an inexpensive student model will do fine. If it's, "She wants to go to college with it," you'd probably want something better than a student model and possibly an instrument with a range to low C, not low Eb.