“I’m selling same products as my supplier and we both advertise on AdWords. We were wondering whether one of us is eating away some market share from the other by doing so, and we end up paying more per conversion than if only one of us would be using AdWords.”
This is a hard question to answer properly as there are a number of different scenarios that could take place and the effects of each will be quite different on your end results.
Yes, competition can drive up prices. If you’re both competing to position your ad in the same slot on the Search Engine Results Page (SERP), then obviously you’re going to be in direct competition with each other and anyone else who is advertising against that keyword, which could drive up costs.
But, if you’re the only bidders on the SERP and not fighting each other for position, then it’ll make little difference on your conversion rates.