I understand why you are doing this. For people without trucks, online ordering is a God-send. And quite unique to the US too. It is the only place I have ever lived where you can get absolutely anything online. Even HVAC parts! In England, this would be so illegal. Heck I even ordered pest-control treatment here once. I have ordered windows, fireplaces and soon will order stairs online, all send freight to my door.
My advice is to phone them up, e-mail them and develop a relationship. The best firms are always the ones who answer all your questions and get back to you quickly. I rarely have problems with online firms where I build up a relationship with a knowledgable sales rep there.
The other trick is to order small first, then big when you know what you are getting. I do this all the time to stop me getting burned too bad.