If you are going to buy anything online that you do not understand or know about, you are taking a risk.
I don't know much about RC models or making such. So I wouldn't think about buying stuff like that online.
If your knowledge about bowling balls, CGs, pin placement etc...is not good, don't risk the money buying online. Because if you get a defective ball, you'll have to take it up with the people you bought it from, not the driller. If you buy a ball totally unsuited for your game, lane condition and skill that's your problem; deal with the people you bought the ball from.
And as far as weird pins and cgs. Yeah there's a very good chance that you will get a strange ball. Not so strange as to be a blem, but bad enough that its a challenge for the driller to lay it out so that you get the expected ball reaction. We get a lot of strange pin to cg to mass bias balls from the internet.
Erin