Very broadly speaking, I would apply the following rating scale:
1. Box store, Amazon bargains, etc. Everything low quality, and the final build, lubrication, and adjustment will vary from suspicious to nonexistent. Can be made to work if you possess decent repair skills and some patience, but not fun to work on due to poorly fitting parts.
2. Some mail order companies that have been around for a while (Bikes Direct) that use mainstream parts of known provenance. There have been reports of problems such as un-lubricated bearings, but a once-over before the initial ride will probably turn it into a reliable ride.
3. Full service bike shop with its own repair business will probably make sure the bikes they sell are ready to ride, and will prefer to sell brands that require minimal effort to get into good working order since they pay double for problems -- once to get the bike ready for sale and again if it comes back for warranty work.
In these cases, the question is: Who is the person who makes sure the bike is OK? In the first case, nobody. In the second case, you. In the third case, the bike shop.