I don't think you realize even now that by posting such specifics on a public forum, you're engaging in highly unprofessional (not to mention self-damaging) behavior, that could harm your client too.
1. Get rid of any spammy/copied content from that website!2. Start with quality content!3. Optimize again your on-page.4. Start working on off-page optimization with quality link building services.5. Repeat points 2 and 4, again and again!We can suggest seostarlet.com for on-page and off-page optimization. They are good at this!
I`m not sure but I think it`s because of spam links. If not then it might be like that Google is losing trust on site. Just have a look at GA and Google Webmaster tools for any message.
Wait for couple for days, If you don't get back your ranking. Then see your indexing in your Google (eg. site:URL). There may be a chance that you hit be Google panda or penguin update. Check webmaster tools for error and remove them. Check message in webmaster tools. Remove Remove irrelevant back links( i.e. bad neighbor) and outgoing links from your website. Recheck Your complete on Page
Hello, I think your client site is only effected by the recent Google updates. Actually, there are many peoples who have suffering with these updates and you must have to know Google also affected by it's own updates. So, ask your client to remove first all the bad backlinks and use the white hat to get his ranking Back.