I cant confirm that but it is definitely true that shop coupons are often at prices larger than betfair and they dont bother to re-print the coupons so you can get arbs, however you will almost certainly be limited at the shop as to how much you can get on. Almost every weekend the Ladbrokes Soccer coupon will have a few.
I sometimes put 20 - 50 quid on a football match when the shop coupon odds are far enough out of line to make it worth my while. Nothing that looks like I'm taking the p**s, just make a few quid. Luckily I walk past one on my home from work when I don't drive. They always seem glad of the business! However I've never looked at their horse odds. Surely they don't keep those static when the online bookies are moving theirs?
Incidently, the bookies in the town centre definitely reprint their coupons. The manager was moaning about it to e last time I was in. Had to chuckle