Both sites (http://seoshop.biz/ and http://plussem.com/) use Google Analytics. So Google could feasibly track who makes a purchase. If you make purchase on those sites and you've recently logged into your Google Webmaster tools or something and then get a load of +1's Google could surely fairly easily see that.
Promoting google+ votes is becoming a very hot business. Using these types of services could have negative or positive affects on SEO.
We just have to see how google treats them. Another place to buy google plus votes is bulkones.com
Will be interesting to see how this evolves over the next few months.
