If I absolutely couldn't get out to "test drive" different machines, I would be doing a lot of online research to narrow down my choices. Would probably start with Amazon, using the price range that interests me and displaying results by "average customer review". I would read all of the Amazon reviews, since they often contain bits and pieces of useful information about a machine. Once I got the brand and model narrowed down a bit, I would check out reviews at patternreview.com for the specific model. I would also run Google searches on the specific brand and model to check out other reviews.
I would consider purchasing from Amazon *provided* it is a sewing machine that is "sold by Amazon" in addition to being "fulfilled by Amazon". When "sold by Amazon", return is extremely easy -- you have a window of time to try out the machine. If anything is wrong with it, return shipping is free. If I simply decide I don't like the machine, I would have to pay the shipping.
AllBrands is another online possibility, but I would check out their current return policies and also current reviews on their helpfulness. They used to be pretty good.
Most dealers will not take a return on a sewing machine (a few exceptions, especially if you decide to "trade up" with the dealer), and a good dealer may no longer be in business when you need help, so buying on the internet is not necessarily riskier than buying from a local dealer.