I had the same problems with 1:76 scale model buses. Quality was a lottery. So much so that I ceased all activity at the beginning of this year, and my shop lies idle, waiting for some unspecified time in the future when these issues might be addressed.
Of the models I had printed, I suppose less than half were of acceptable quality. I never sent any back, as I understand that while sending one or two back may be okay, sending lots back is totally impractical, and costly.
I can make some use, with difficulty, of the sub standard models I received. But they are totally unsaleable to anyone else. I am having a hard time selling Shapeways as a good idea among my own modelling community, particularly with a queue of inquiring customers, and my shop effectively closed until further notice.
Specified print orientation will go a long way to solving the issues. A softer material more suitable for railway/aeroplane/vehicle models, but priced closer to WSF, would be a huge step forward too.