A true loss leader isn't really necessary, since an accountant's or lawyer's clients -- almost by definition -- have problems judging the quality of the work. It's every consultants core problem: Clients can only judge the "product" after they bought it, sometimes not even then.
This is why reputation and (perceived) authority is so important for consultants.
The usual ingredients to get authority and reputation is time (years spend in business), size (being in the top 100), or word-of-mouth: being recommended by previous clients or independent magazines, journals, TV reports, etc. A less known ingredient is spending money for apparently unrelated stuff: exclusive office furniture, exclusive business cards, an exclusive car, watch, suit, etc. -- even looking "attractive" (fit, groomed, etc.).
Accountants building their practise obviously have (nearly) none of the above. Thus, they need to do other "expensive" stuff. Some tips:
- Use a high-quality monotone design with white space (and maybe gradients).
- Use good (!) images of the accountants or lawyers themselves, directly on the front page. Monotone images look more "artsy" and expensive.
- Use a blog/news section for creating the impression you can afford to have the site actively maintained. It's also good for SEO.
- Display a telephone number as a means of contact. Have a secretary (or someone else pretending to be one) answer it.
- Make guest posts in other blogs or online journals. The more exclusive and prominent they are, the better.
- Find communities where your potential clients discuss your area of expertise. Join the conversation and help. As a professional, you'll often quickly gain a good standing, since nearly everybody else has less natural authority.
- If you want to do Adwords, use a high budget. It doesn't help if you appear for one keyword, only, but not for a closely related one.
- Don't forget the usual means: Speaking at conferences, business cards, telephone book, etc.
Depending on the preferred target audience, you need to "fine-tune". For example, if your clients will be farmers, you shouldn't appear too exclusive -- not even online.
Hope that helps.