Better yet,
Allow customers to buy hashpacks at lower rates but charge us more fees per month.
Right now a 50Gh/s hashpack is about 20btc.
I'd be willing to pay 8% or 10% in fees a month if the hashpack is re-rated at 10 or 14BTC. It might be an idea worth considering.
Seriously considering this. do not be surprised if you're the first to know if it is implemented.
I would not be surprised if you did, it would make you quite alot more than the pool itself would. If you manage your finances correctly, there wouldn't be any issues.
Make sure to contact BFL (Or Avalon) and see if they are willing to offer you any discounts for consistently large purchase orders. I believe Avalon will, I do not know if BFL will.
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You need to work on the issue of redeemable hardware. If you can assure this, (the customer pays for any shipping costs) then you are set. People will eventually copy your pool when they realize your system may work.
The reason behind the idea of "redeemable" hardware is that you can assure customers it is there whenever they "need it". As you grow in reputation and confidence your customers will eventually (likely) decide it is far better to keep their hardware hosted with you than in their own homes. Eventually, they will not be able to host it in their own homes. I know I can't host more than 3..maybe 4 at most.
If someone wants to pull their hardware from the Hashrack® they could contact you in email, pay off the discounted difference or any fees pending on the hardware for the month...and then pay for the shipping charges to get it delivered. It is important that you get some kind of (non-permanent) labeling system. Like magnetic labels, #001 or whatever, so you know which one is the customers.
After people have confidence you are here to stay for the long haul; they will probably just keep it perpetually at the colocation facility you are doing business with...through you. You should also limit how many "redeemable shipments" you are willing (or can do) per week without straining you or your staff. If it is 50 slots per week, it is 50, no more no less.
Anyway, you have a very good idea going for you. I hope it takes off and it keeps you profitable. I frankly do not see how it couldn't.