YMMV, but my experience is that dealerships do not offer you nearly as good a deal by email vs negotiating in person, getting close, then getting up ready to walk out (and often walking out, leaving your contact phone number behind). The reasons are
that they do not see you as serious buyer until you are there and ready to sign,
that they are very reluctant to put their best offer in writing likely to be used for leverage elsewhere,
and that they do not have the sunk cost of the time and effort spend negotiating to pull them toward the deal.
YMMV, but my experience is that dealerships do not offer you nearly as good a deal by email vs negotiating in person, getting close, then getting up ready to walk out (and often walking out, leaving your contact phone number behind). The reasons are
that they do not see you as serious buyer until you are there and ready to sign,
that they are very reluctant to put their best offer in writing likely to be used for leverage elsewhere,
and that they do not have the sunk cost of the time and effort spend negotiating to pull them toward the deal.