How to upsell on fiverr

ive been doing some basic SEO gigs on fiverr for about 2 months now, mostly link-building and social media. things are finally getting rolling to the point where i have a solid reputation there and am getting a good number of orders every day plus a handful of people coming back for a dozen re-orders etc.

i am shit at "marketing", being more a tech/programming geek. i know i really should be up/cross-selling them something or directing the repeat customers out of the fiverr ecosystem to make more cash and solidify some more lucrative and long term deals.

thoughts on the best ways to do this in general? what to offer? where/when to offer?
and specifically on fiverr as it is against the TOS?

I don't know a whole lot about fiverr but, could you just put something in your gig that enable them to contact you about something "specific" that they would need to talk to you about, then just hint at your website or something... Like I said, I don't know a whole lot about their TOS but, just throwing out some ideas