Most tickets that have obstruted views have that information printed on the ticket, at least it does for hockey games down here.

Print out the seating cart for the ballpark, and use that as a guide in determining if you want to pay $50/seat from onsite scalpers. Believe it or not, most people selling a ticket or two are not out to rob you, just make an extra buck.

You can also try to get tickets off of www.craigslist.com and click on Boston. It a localized version of ebay. I've gotten Cubs tickets this way when I go home to Chicago (sweet home!).

Good luck.

CaryB