The spread: buying low, selling high

Every arbitrage business, from a currency booth to a fruit trader, lives or dies on one gap: the difference between the buying price and the selling price. In search arbitrage that gap is called the spread. This lesson teaches you to calculate it, because nothing else in the business makes sense until you can.

A currency exchange booth at an airport buys euros at 88 rupees and sells them at 92. Four rupees per euro does not sound like much. Multiply it by ten thousand euros a day and it pays the rent. Lose two rupees of that gap and the booth barely survives. Search arbitrage has the same shape: tiny per-click margins, large volumes, and very little room for error.

The buying price: cost per click

On the buying side you pay a traffic source for visitors. The usual measure is CPC, cost per click: total ad spend divided by the number of clicks. If you spend 200 dollars and get 1,000 visitors, your CPC is 20 cents. Some platforms charge per thousand ad views instead (CPM), but you can always convert it to a cost per visitor.

The selling price: revenue per click and per visit

On the selling side, not every visitor earns money. Only some of them click a search term, and only some of those click an ad. Two numbers describe this:

• RPC, revenue per click: what you earn each time a visitor clicks a search ad. This is your share of what the advertiser paid, after the search engine and any feed provider have taken theirs.
• RPV, revenue per visit: total revenue divided by all visitors who arrived, including the ones who clicked nothing. This is the number you compare directly with CPC.

A worked example

The numbers below are invented for illustration. Real ones vary widely by country, topic and season.

1. Buy 1,000 visitorsYou pay 20 cents each. Spend: 1,000 × 0.20 = 200 dollars.
2. Some click a search termSay 40% of visitors tap one of the related search links on your article. That is 400 people reaching the results page. This share is your Lander CTR.
3. Some click an adSay half of those 400 click a sponsored result. That is 200 paid clicks, each one a monetised click.
4. You are paid per ad clickSay your share averages 1.40 dollars per ad click. Revenue: 200 × 1.40 = 280 dollars.
5. Work out the spreadRPV = 280 ÷ 1,000 = 28 cents. CPC was 20 cents. The spread is 8 cents per visitor, or 80 dollars on the day.

How fragile the spread is

Now change one thing. Suppose the traffic platform gets more competitive and your CPC rises from 20 to 26 cents. Spend becomes 260 dollars, revenue stays 280, and profit falls from 80 to 20 dollars. A six cent change wiped out three quarters of the profit. If CPC reaches 28 cents you are at break-even point: you worked all day for nothing.

The same happens from the other side. If advertisers decide the visitors are not converting, they bid less, RPC falls, and the spread closes without your costs changing at all. Operators watch both prices every day, often every hour.

1. An advertiser pays for a click: Someone clicks a sponsored listing on an arbitrage page. The advertiser’s account is charged $1.00. Every figure in this flow is an example: real shares differ by contract and most are confidential.
2. The search engine takes its cut: The engine supplied the advertisers, the auction and the billing, so it keeps a slice first. Say it keeps $0.30 and passes on $0.70. What it pays out to partners is its traffic acquisition cost.
3. The feed provider takes its cut: Most arbitrageurs do not contract with the engine directly. A feed provider does, and shares the feed onward for a revenue share. Say it keeps 20% of the $0.70: $0.14.
4. What the arbitrageur receives: The arbitrageur gets $0.56 for that ad click, its RPC. Only about half of its visitors click an ad, so average revenue per visitor (RPV) is $0.28. That is its gross revenue.
5. Most of it was already spent: Each visitor was bought from a traffic source for $0.20, paid up front. So the largest single share of the arbitrageur’s income goes straight back out to an ad platform.
6. The spread: $0.28 in, $0.20 out: $0.08 per visitor is the spread, before staff, tools and content costs. Out of the advertiser’s dollar, the business that built the page keeps the thinnest slice and carries the most risk.
7. Invalid clicks unwind the chain: If the engine later decides a click was an invalid click, it credits the advertiser and nobody downstream is paid for it. The arbitrageur sees that as a Clawback (revenue deduction), even though the $0.20 spent on the visitor is gone.

The spread is shared before you see it

The advertiser's payment is split several times before it becomes your RPC. The search engine keeps a share. If you reach the search engine through a feed provider rather than directly, that company keeps a share of what is passed on. What arrives is your revenue share. Google has only once published a standard rate for its search product for publishers.

Three things that quietly eat the spread

• Revenue adjustments. The figure you see on the day is estimated revenue. After invalid clicks are removed it becomes finalised revenue, which can be lower. A deduction after the fact is called a clawback.
• Running costs. Tracking software, writers, designers, staff and payment fees all come out of the spread.
• Time. You pay for traffic today and are typically paid by the feed weeks later. That gap ties up cash and limits how fast you can grow.