There are endless ways to promote your business. There are WiX Facebook design groups, generalized social media design groups, you should obviously have your own website touting your skills, there are plenty of sites like Upwork for hourly work sites where people are looking for website design experts specifically in WiX, sometimes not. If you are good with sales, you can convert them to WiX!
For the naysayers, ask what they like about their current platform and then make the comparisons from there. The issues that people “think” they have with WiX are often imagined or outdated such as the SEO. The SEO has come a long way as have the apps. WiX is a major competitor now.
With coding options, hundreds of templates and literally thousands of options, designing on WiX is not something that is “less then.” Not everyone has time or interest to build a site from scratch or the aptitude for it and being able to brand someone’s message and drive their customer base to their site is no less important on WiX than it is on SS or WP.
Of course I’m not shy or quiet in how I feel about the ridiculous price jump as of late. That corporate greed is a major blow in what built WiX’s customer base, the low-cost alá carte platform where everyone could come in and build their site at relatively no risk. Now the price point is where competitors can get a good foothold and offer many of the same things WiX. You need to sell yourself in your design skills and accessibility to overcome the economic advantage we all lost as the top selling point when WiX decided corporate greed was more important than customer loyalty.