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Pools do deduct fees from your rewards already.

You are right, I thought grcpool.com had no fees. However, the fee is so small (0.05 grc per payout) that it is almost free.

You make a good point that definitely has to be considered. I think it is also important to keep in mind that transaction fees, as an example of what MERRC fees might look like, are only 0.01 GRC (recommended).

MERCTrX is likely going to use only so much resources as standard TrX, so they should undergo the same fees. @jringo's "side-staking" somewhat complicates fees policy.
Regardless of both, more extensive talk on the topic of fees will be needed (TrX spam, blocksize...).