I think in many parts of the country you can still make a profit at craft fairs. However, you have to know your niche and be familiar with the shows in the area. Not every show is a fit for every person. You need to decide how much soap you would need to sell to be able to make the show profitable and then making the decision of whether that is possible. If it isn't possible the first year would it be in the second or third when there would be repeat customers. I do well but limit my shows to ones with non-profit promoters that cater to a family atmosphere. I like double booths so that more than one customer can be at the tables (even though it increases my costs). You have to decide how many bars you could actually sell each day. It takes physical stamina standing and each sale takes time. I do a couple of large shows and I can sell 300 bars in a day but I am totally worn out. I couldn't have done my big shows the first 5 years I was selling soap. It took time building a reputation so that each year I see the same people and they are looking for me. It took time for me to learn what customers want and how best to manage my booth to sell. As you learn from smaller shows it makes it easier to decide when/if to pay the larger fees.
I think shows are the best way to gauge what scents customers like and what they want in their products. For me one of the joys of my soap is how many friends I have that years ago were only customers.