There are some forms of advertising you really shouldn't try to handle yourself.
The complexity of some forms of advertising, particularly mass media and advertising campaigns, is not only expensive, but the production times and related costs are potentially horrific.
What you shouldn't do for yourself:
Why you shouldn't do it yourself:
Broadcast advertising on mass media.
Broadcast advertising is very big money. There's almost no such thing as cheap broadcasting, except on public broadcasting and local radio.
The process of buying time is much the same as any other form of buying advertising space, but there are other issues:
Using an agency, you get better market analysis, and you may also find they're not too keen on some forms of broadcast advertisement.
National or large scale promotional campaigns.
These are big by definition, and need costing and planning to work properly. Do NOT attempt any major advertising campaign on your own, even if your local ads are working well. You'd be better off just doing more local ads.
Use an agency, or a consultant, but don't commit to that sort of expenditure without thorough costing and evaluation from the ground up.
Market research, beyond very basic methods.
Marketing is a science. Market research isn't just asking if people like your products. It's about researching people's needs, and their market orientation, and buying behavior.
Market research works on an economic basis, identifying your clientele, and analyzing their receptivity to products, prices, and their other criteria for purchase.
You can get useful feedback direct from your customers, and in many cases that's most of what you need. If you're planning any big business moves, however, you'll find that you need more than opinions.
Use a market research company or qualified consultant.
Product testing using members of the public.
Product testing is one of the basic methodologies of all industries. Products are tested for defects, uses, bugs, like beta testing for software, and a range of other things for marketing purposes.
The main issue in product testing is public safety.
Try doing your own product testing, using members of the public, and your insurer will hike your premiums up overnight, or maybe cancel your policy.
You may also find yourself in court for a violation of health or safety regulations.
Many of the ads you see on TV about people 'trying out new products' relate to products known to be safe to use after thorough safety testing.
Even laundry powders can cause dermatitis, and serious infections.
JUST DON'T DO IT.
All product research should be carried out by professionals.
There are often statutory requirements for product contents and safety warnings, based on chemical or other hazards.
No product should be allowed anywhere near the public for market evaluation until you're sure it's safe to do so.
That's after product safety certification, and never before it.
Always use a qualified product testing and certification process for any product intended for public use.