Best place to buy?

What are your thoughts on buying wine? Are some places better than others? Not just talking about price - but as a new wine enthusiast I wonder how well wines are stored by sellers like groceries including TJs and Costco, Total Wine discount places, and anywhere else. If we are supposed to store wine on its side, why do all these stores have the bottles upright? Does it matter to you that the store is not at a great temperature or the bottles had to be exposed to heat and cold in shipping? Am I being silly or should I buy from other sources?