Corinvid, don't be daft. Don't turn down work just cause you've never done it before. Look at the place, try to work out how long it'll take and times that by the hourly rate you're happy to work for, bearing in mind that commercial work is more competetive than private and some one will try to undercut you if they can.
Also, the insides are only dirty on the first clean, assuming they have them done each time the pub's cleaned. Most of the pubs I clean are done each fortnight, inside and out downstairs and outside upstairs, ie, their living quarters.
Get all the commercial work you can. It's harder to get than private, but it gets cleaned in all weathers.
Take the leap mate, or you'll never know what to price them at
