THIS!!!
Let's just say that you do pay 50% more (usually the B&M are pretty competitive though) and you end up paying $150 for skimmer X and it works great because someone with expertise guides you into the correct product and you are happy.
Contrast that with buying online because of what you heard on the internet, it's quite common to save some money on skimmer A $50, but months later it isn't working right, so you buy skimmer B for $75 and it's better but 6 months later it breaks and you end up buying skimmer X for $100. By this time you are $225 and 8 months of frustration into it.
The common thing is you step it up and spend $350 on skimmer S"¦ and either it sucks the salt right out of the water or it works just fine and you ended ups spending $350 when $150 would have yielded the same results.