PPC Primer is written by web developer and search marketer 
Quick comparison between natural and paid search
Natural search:
- Prominent page positioning
- Slow results
- Moderate trust level
- Difficult to attain top positions
- Traffic volume based on position for various keywords
- Low to moderate cost
Paid search:
- Less prominent page positioning
- Fast results
- Less trust (users perceive paid ranks as being "bought")
- Easier to achieve top results (provided the budget supports this desire)
- Traffic can be quite high for all keywords
- Moderate to high cost
