I would say its not about margins but minimum viability. If your 10% margin equates to 10p then probably not going to be worth adwords, but if your 10% is £100 then adwords would be, potentially, great. Obviously there is a massive range of scenarios in between.
Some tips
- Use google shopping ads where possible, for ecommerce they seem to have better conversion rates.
- Do not go direct with google, the price of an adwords manager, should if they know what they are doing, be less than the savings vs how they would run a campaign.
- Always go with the same company for adwords and your website, they need to know the system and be able to quickly add tracking code, split testing, landing pages etc. If you have two different providers you will inflate costs almost every time.
- Make sure you have ownership of your adwords account, this is vital to ensure you know how/where your money is going. Check the journal to keep an eye that they are actually doing something.
- Make sure you consider all forms of marketing together, adwords for ecommerce is only one part of the puzzle and it will require very good after sales service to turn the more expensive adwords customers into repeat buyers which will drive a better return on investment.
- Track everything, do not spend a penny unless you have google adwords conversion tracking correctly setup with your ecommerce so you can get proper ROI numbers.
Best of luck and if you need any specific advice feel free to PM.