@Patrick M.
Your decision to disclose or not is usually an issue regulated by your state's real estate commission. That's the same group who licenses real estate agents, and authorizes training for the real estate industry.
If a Realtor® in your state has a disclosure form that they commonly use discussing mold or other environmental issues, then your decision to NOT use one makes your transaction "unique" and may also open you up to certain liabilities. (I am not an attorney, but I do expert witness work FOR attorneys on a variety of mold-related issues.)
Often times, I tell folks to take photos of how bad it was in the beginning, how it looked when it was all cleaned up, and then how the finished product (rebuilt area) looks today. That's good documentation for any buyer.
Now whether you choose to do it yourself or to use outside help is another important issue. It's like flipping a coin where one side says "do it!" and the other says "hire it!"
Outside Help
The first side of the financial coin that you're considering flipping involves how much you will pay to have a third-party do the work for you. If you choose to go that route, then ideally, you'll want a consultant to come in and test (to prove that the problem is/isn't isolated to the area with the obvious mold), and you may even want them to write a "scope of work" to complete the remediation (mold tear out language). Then, you'll take the scope of work to a remediation company who will do the actual work (tearing out the mold contaminated materials). When they say they are done (and they confirm that they followed the scope of work) then you call the consultant to come back in and retest the areas. The consultant will inspect the work that was done, test the air, and give you a report that all is well (hopefully). That "clearance report" can then become part of the sales documents showing the buyer that while there was a problem, you fixed it and they have no reason for worry.
Do-It-Yourself (DIY)
You will save money if you do it yourself. You can also screw it up MUCH worse if you don't know what you're doing or you aren't careful in all steps of the process. If you do it yourself, you will pretty much eliminate the pre-test, remediation work, and post-test costs. But if you don't follow some kind of written guidelines, you are sure to screw it up. What's your option? I'd say review this document put out by the US EPA and decide for yourself how much work you really want to do.
A Brief Guide to Mold, Moisture, and Your Home
This first document discusses how moisture happens and how it supports the growth of mold.
Mold Remediation in Schools and Commercial Buildings
This second document is the "all encompassing guide" on how to manage and remediate mold from all types of buildings (residential too). This is the common type of guidance that a "scope of work" to remediate mold will include.
Your Sales Price
You asked if the presence of mold will lower the sales price. It shouldn't! I guess it depends on how hot the market is in your city.
I am from Texas. We've lived with the "toxic mold" issue since 1998 (and earlier). I would say that having had mold somewhere in a home is not the same type of issue that it 16 years ago.
Buyers have a better understanding of what it is and what it can do.
Sellers have a better understanding of how to market the home.
Buyers usually know that if it's done right (professionally) then their cause for concerns is pretty small. Most buyers ... not all buyers. You just have to find the one who wants it!
Sorry if I meandered around this answer. It's not black and white, cut and dried, or ying and yang! While we do know what to do based on years of experience, every situation is different.
If you'd care to show us some photos or provide more details then I can certainly give you a more detailed answer (he said facetiously).
Good luck!
Travis West
CIEC - Certified Indoor Environmental Consultant, Certified by the American Council of Accredited Certifications
MAC0325 - Licensed Mold Assessment Consultant, Texas Department of State Health Services
Keywords: toxic mold, black mold, water damage, mold remediation, stachybotrys, mold disclosure