Basically the whole idea of sliding as opposed to flipping or swinging (snigger) is that instead of simply doing one trade once at the top and bottom, the price will rise and fall only a few gold pieces each day over the course of the week.What this means is if you solely rely on buying for minimum and selling at max you will have a problem while you wait ages for the conditions to be met...sliding is the alternative.
[Insert random Numb3rs imagery here]
Imagine a nature rune starting at 200 gold and it rises 3 gp each day to 220 yet its max price is generally 10% over this...we can buy our nature rune for 203 (since we already know the most common buy price previously) and get them fairly fast and then simply sell at max-3 since because everyone now had to match your offer they have to offer more to buy...you simply sell it back to them.
So what you have is a system such as:
mid 200 buy 203 sell 220
mid 203 buy 206 sell 220
mid 206 buy 209 sell 220
mid 209 buy 212 sell 225
mid 212 buy 215 sell 223
mid 215 buy 218 sell 221
When the price starts to drop simply reverse it, buying at min and selling just under mid...this allows fantastic profits over time
Say you can buy 4x25k per day
Thats 100,000 x 17gp profit just on the first day for 1.7M profit!!
Continue that over the week and though it is likely you will get shorter odds it will start to tell you when it is going to reverse simply due to this mechanism.
Of course the higher the price goes over time the shorter your profits will be as a result due to that line that everyone carries in their head telling them the price of a rune...however if you time and price it well you can get around this quite easily...all you need is luck at choosing the exact price to buy and sell at...
Of course the nature rune is simply an example, it works well with lower priced items that flow up and down regularly rather than those that bounce everywhere like a constipated camel on vindaloo...if you have the spare cash and can identify good buy and sell prices for a certain product, try it, you will not be disappointed :)