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It's not bad advice really. You can't just go to Walmart or Target and buy any bike and expect a good fit. Humans are different and we all have different needs. Those aren't obvious to a noob. The sales person can really help find the right bike, size and accessories.
In terms of price, there's a reason why the Walmart bikes are cheap. Also, once you know what you need, there are online options. I wanted a bike like a Trek model that was selling for $2,000.00. I found the very highly rated Nashbar brand which can be purchased online and got the bike for $600.00. I've ridden it thousands of miles and it fits my 6'4" body perfectly. I wouldn't have known what to buy had I not gone to a local store. I still buy a lot of accessories, seats, etc from the local store so that they I can do my part to help them survive.