There are a lot of resources out there. Emailing dealers is obviously one option, but takes a little effort unless you use something like Edmunds service. I went to local dealer's websites and looked for internet or fleet sales email addresses, which took time. If there wasn't anything, I'd send to a general mailbox or the sales manager. I told them what I wanted (model, trim, color(s), etc.) and when I was looking to buy (keep it short-term and before the end of the month will speak to them for monthly bonus numbers...you may want to email with a week left in the month). I asked if they had it in stock and could provide me a all-inclusive "out the door" price. No messing around with fees and nonsense. If you want to charge me a $500 doc fee, then roll it into your offer to me.
Some dealers won't answer, some will toss out a weak offer, some will try and pressure you by saying it is good for the weekend, others will actually just put out a good offer. It will at least give you an idea of where the pricing is. Then compare it to invoice or whatever numbers you have. TrueCar used to give you "dealer cost", but they don't offer that after getting sued. Some dealers will try to get you to come in to negotiate further, others will negotiate further on email. I've read from professional car negotiators that picking up the phone can help show you are serious when you get into the later stages of negotiation. Obviously showing up with a checkbook would help too. From my time selling cars, I also try and give the salesman who may have helped with my test drive a chance to get the deal in the end unless they were just terrible.
For popular models, I'd also check out the Edmunds prices paid forum or a forum for that model. An Accord should have a good forum somewhere with people sharing sale prices.
As far as method to buy, cash does one thing: shows you are ready to buy. When I sold cars the sales manager was always hesitant to give a strong number to someone who might be a tire kicker looking to go across town. If you say you can pay cash today if they meet your demands, they will be more aggressive with their pricing. Having financing in hand helps too, as then they don't have to worry about losing a sale when the banks don't bite on the loan. Yet they do make money on the loan, and financing also offers them an avenue to bump a rate and make money. Hence why you never deal in monthly payments and bring your own approval first. When I bought my Subaru, I had 1.79% in my pocket and they beat it with 0.9%. That is what you want if you finance.
Finally, with something like a 2013 Accord which may be relatively "hot" right now, you may do well with a buying service like Costco. Costco's discount is not so amazing on cars where deals are to be had, but on models with a lesser average discount, they can get you the same deal with less hassle. Edmunds has a service. Most banks have a service through TrueCar. I'm not sure how good TrueCar's offers are these days. The "target prices" they offer are pretty weak from my shopping experience.
