There is a major difference in parts and where the vendors get them... it just depends on the parts. Some items such as the bumpers, there may only be one or two suppliers to the vendors... other parts such as seals or wiring harnesses or interior parts, like seat foam, covers etc... there is a major difference, and it's a good idea to ask where they are from, and who manufactures them.
Like I said, Ames... being bought out is changing rapidly, and it's starting to show. In some cases they can't get the same deals on the same top notch parts, so they are starting to go with what they can get type of thing... so again... ask all the questions up front.
If you do find a good deal on a bumper, please let us know what you think of fit and finish in the end.