Do flash sites make it difficult to get high rankings on search engines?
Do sites created using Wix (flash based DIY sites) have any difficulty in achieving good rankings?
What can be done to resolve problems?
I've just answered a similar question minutes ago. You can read it here.
As for Wix, I' not familiar with it, maybe someone can offer more inslights. You might want to check out http://seomywix.com for a start.
In your generated HTML add some basic SEO markup, stuff like h1, a p with a class of description, some other headings just the basics. results are not spectacular but it does the job.