Of the 1,000,000 or so bitcoins traded each day, at most only 1800 of those come from miners. It is not likely that miners as a group have a measurable influence on the price.
That, and the far majority of the minted coins won't even end up being sold on the regular market at all. In case of the largest farms generating the most value out of their efforts, they very likely sell coins outside the regular market when needed or when they accumulated enough coins to fill high value orders.
If there is one thing miners want to prevent, then it's their supply affecting the exchange rate. The smaller miners liquidating their holdings are too insignificant to even dent the market.
Once the block halving has done its work miners will form even less of a problem, especially when you calculate forward how this market will attract more capital. It will only further solidify the market.
