In the last few years I have seen almost all type of the attacks (SEO spam, injected malware, fake jquery, backdoors, spam sending scripts, etc.) and all of my clients were satisfied with the results. Nobody contacted me with reinfections so far!
After the cleaning I will secure your site with iThemes Security and Wordfence.
If you want to read real client testimonials just check out my Joomla cleaning gig.