How does being on the first page of google affect sales?

It depends on your niche and the quality of your website. Being on the first page will get you more clicks than being on page 2 or lower (obviously), but not necessarily sales. People have to like your site -and it has to be a keyword that can be monetized.
It also makes a big difference what part of the page you're on. The first few listings on Page 1 are a lot more valuable than those on the lower half of the page.

Well that depends on the niche and keyword/phrase.

Remember that 60% of people click the #1 result, about 20% click number 2, 5% click number 3 and the rest is divided to make a really rough example (not accurate but the differences between a number 1 and a number 5 slot are HUGE to say the least)

Well being on the first page of Google will get you much more traffic to your website but that doesn't always means that the sales will get higher too. I mean if you don't have a good sales page almost no one will buy anything. Also there is the product you are selling. If the price of the product is insane or the product can be found cheaper than not many people will buy regardless of you being on the first page on Google. There are many variables to be taken in consideration when it comes to the measuring of the percentage of the sales, not just the ranking in Google.

I found this on Google for you to give you a rough idea:
How Much Difference Can A First Page Ranking Make? | JanetBrune.net

There is no way to answer your question without more detail.

You are asking for ROI. Firstly, how much have you invested?

Next we need to know how much traffic page one is getting.

Another major contributor is the buyers intent on the keyword you are going for.

If you are targeting "golf tips", the majority of your traffic is going to be searching for free golf tips.

If you are targeting "online golf courses", a larger percentage are going to have their credit cards out and ready to make a purchase on your website.

So as you can see, there is a LOT of variables about being on page one. Some times you may loose money, if the keyword research, onpage content, or SEO campaign has not been thought through.

Other times you can make a LOT of money and increase your consistent sales.

Other thing to consider is that the average searchers in some niches will scroll past page one, whereas the average searchers in other niches will only view page one. Who knows why, it's just different mindsets in different niches.

There is no scientific answer, unless you know ALL the variables (which is very much on a case by case basis), even then it's only an estimated guess.

Cheers,

Vague is an understatement. You could be on the first page of Google and not even get a single sale for an entire year, but you could be there and make millions as well. The subject/niche makes a huge difference, the keyword phrase makes a huge differences, and so does the competition. Also, it makes a difference if you are first, second, third, or lower as well.

Too many variables to give real statistics in general. This is going to be hard to get a specific set of stats for. However, if you narrow it down to specific niches you could find stats.

Benjamin Ehinger

Well basically in order for people to get visits to your site...they first and foremost must be able to see you...Internet users often believe that these results on the first Search Engine Result Page, or SERP, must be the best websites available that match their search.For websites that appear on the second Google SERP, the number of web users who actually visit one of these websites drops to only around 10-15%.The reasons to achieve a page one SERP ranking are clear; over half of all search engine users visit one of the top three listings on page one of a SERP.