Yes, power feeding is when you feed as much as you can to your snake (without causing a regurge) in quantity, prey size and frequency in order to get the snake to breeding size as quickly as possible. Of course, there are those who do this because they just can't wait to see their snake full grown, but mostly it is done to be able to breed sooner. This is really not healthy for the snake and can, and often does, cause obesity and obese snakes are more prone to breeding problems as well as a shortened life span.
I don't think a pet shop owner should be telling customers it is ok to power feed their snakes, but, then again, it doesn't surprise me.
I definitely suggest keeping on a feeding schedule of approx. 5 days while young and moving to 7 days when a year and a half or so. A fully-grown, large snake can even to every two weeks on one mouse and keep in great shape. Feed only as large a prey item as makes a visible "bump" in the belly after eaten and up the prey size when the bump starts becoming less noticeable, in fact, go to two of the prey size you are feeding for about 3 - 4 meals before you up to the next size. Your snake will not grow as fast as the power fed ones, but it will also not become obese and life a longer life.
Also, remember the "48 hour rule" - don't handle the snake for 48 hours after each feeding. The food is normally digested enough so no stress regurges occur. Sometimes, however, you will notice that the bump is still a bit visible after 48 hours, if this occurs, wait another day before holding. Sometimes if the prey was a bit larger than normal or the snake didn't stay in the warmer temp side, the prey will take longer to digest.
Have fun and congrats.