can you expand on your question its a bit loose.
there's adwords, affiliate, buying banners on other websites, seo techniques, facebook feeds, google+ etcccccccc
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buying banners on other websites that are VERY targeted to your market works for me, mostly its "pay per impression " not PPC, but the success is down to less then 1% on impression so you need to do your numbers with there charges.
its REALLLLLYYYYY hard to monitor as most sites don't have a clue how to set it up properly.
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on the other side of the coin i sell banners on my sites and its been very successful for @ 10 years now, both for me and my clients.
i use
it use to be VERY simple but its getting more technical now but with that comes extra benefits ( i liked it more when it was simple ! )
i still use it and its FREE, i use it and then promote it using
HTML:
http://www.interspire.com/emailmarketer/
which has become expensive in my view but i make good money out of it i disregard the cost now.
what i find is by using these 2 systems which cost me more TIME to implement but i am in control, i don't have this BS 30 day cookie issue and i make 30 times from it that i do from adwords/affiliates............ but now i am off track of the question.
paid traffic: my opinion is be careful and monitor the results, use short term " dip you foot in the water" methods, push back to people you are paying and say " this isn't working" if its not.
as for me selling my webspace to my clients they definitely get a good return as they renew EVERY year.
when i buy a banner on someone elses website i've been happy but not " OHHH WOW " but my break even point is low at $100p/m so i don't go out and spend heaps of money on them.
tim