I'm trying to use the extensions update element of your component and I got a security warning on the ZIP file I tried to upload which happened to be a valid JED file and then in addition it does nothing when I try to download the latest version of the file following a check for updates.
IMHO your product is simply unfinished (see other tickets) and needs far more work prior to taking money from users.
what's you exact Joomla version? 3.4.4 I guess.
In that version Joomla changed they API about file uploads, blocking packages with PHP code.
I just release a new dev release, can you please install it and confirm the fix?