I have purchased three themes in ThemeForest and have had bad experiences with two of them. Without identifying the specific products, I can list some of the problems.
Two of the themes required Child themes which were not contained in the purchased zip file. I didn’t figure it out until I found I could not get things to work as expected. In the case of one author, I didn’t find out there was a problem until some months later, so I ended up paying for “support”. That support experience was not pleasant. The author was condescending and rude. On two specific occasions I asked him what I should do to fix a problem only to find that he had done things I specifically asked him not to do. In the first case, he switched to the default 2017 theme. In the second situation I asked him what I should do to correct a problem but since I would be out of town with limited access, I asked that he PLEASE not do anything to cause my customer to again ask “What the heck is going on with my web site”. What did he do? Yes, he defaulted the installation so that all my SEO work and customer customization was gone. Again, I relied on Rackspace support to restore the site from backup. We still have not resolved the initial issues with portions of the theme not displaying as advertised.
A second theme has to do with online video training. This theme has so many problems I can’t see how they could consider selling it to the public. The author claims high popularity of the theme. From my experience there is no way that claim could come close to being valid. After weeks and months, the site is still not ready to be public. Database errors, conflicts with plugins, a certificate that showed time where the date should be, strange wording (translation from another language), and on and on. These people could not have tested this product for these issues to still exist. You can’t just tell a customer to ignore update notices from WooCommerce because it will result in a total collapse of the web site. .
Month after month, back and forth, problem after problem to the point where I am ready to forget about both of these and find other resources. Bad experiences two out of three times and I am not likely to make any further investments in anything in ThemeForest.