If a restaurant cannot accommodate your (very)large party, PLEASE DO NOT TAKE IT PERSONALLY.
No restaurant would EVER voluntarily turn people away (HI! YOU'RE WALKING WALLETS! PLEASE DROP CASH HERE!).
HOWEVER, if you're asking for a party of 12 or 13 or 14, odds are that they won't be able to seat all of you at one table. Why? MANY REASONS! The restaurant may not be large enough, the seating layout might not be moveable, the kitchen might not be able to handle such a heavy load, THE LIST GOES ON!
But it is not - REPEAT, IT IS NOT because they don't want your money!
ON THE PLUS SIDE!!! *smiley face goes here* THERE MIGHT BE OPTIONS!
The best case scenario is that they can, through some miracle, be able to handle your huge party. Odds are it will either be early (between 5:30-6:15) or late (8:30 or 9). DON'T GET PISSED!! To guarantee the best service that you and your guests deserve, it needs to be when the kitchen and servers will not be over-run with other guests. DOESN'T THAT SOUND NICE? DON'T YOU WANT GOOD SERVICE??
Not the best case scenario is that they can't seat you all at one table, but could split up the table into three groups of smaller parties. HOWEVER - odds are good that while they will do their best to make sure you are seated close to each other, without prior knowledge of how the rest of the night is going to go, how the tables are set up, how big the dining room is, it's not certain that they can guarantee that. DON'T FREAK OUT!
The last choice is that they can only handle your large party as a private dining event. It'll be more money but you'll probably get exactly what you want. Sooooo - do you shell out the cash to make sure you get what you want, or will you complain loudly to whomever listens that (because you are cheap) this damn restaurant wouldn't give you what you RIGHTFULLY DESERVED?? hmmmmmm
Oh - protip: being passive aggressive to the reservationist, saying such gems as "Gaaaawsh, I just don't understaaaaand why you won't give me what I waaaaant. I mean, we're giving you moooooney and EVERYTHING. Why would you turn us away like thaaaat???" after the kind reservationist explained why they are unable to handle such a large party without breaking down a wall and doing some major remodeling, WILL NOT GARNER YOU SYMPATHY. In fact, it will cause the reservationist to hate you more and probably do less to help you out.