Over the last decade I've received almost daily calls offering me the opportunity to invest in Oil Wells. Now, it's Marijuana Farms.

The Oil Well guys got nowhere - I inherited a small oil well investment so I know better. You can never sell it, because there's no way to value it, even if it's actually pumping oil.

Marijuana? That's what you call a "severe risk investment". Aside from the obvious risks, if you read the fine print, the guys selling the investment have all the rights, and the people they sell to have none.

. . the "buyer" gets a quarterly share of the profit from the oil pumped from the well, proportioned to the number of shares - IF the well actually produces oil, and for as long as the well produces oil.

It is very difficult to sell such an investment, because it is impossible to value it. The well usually yields at a varying rate and could stop producing entirely at any moment.

Most guys offering such investments usually present them as an income source combined with a tax write-off. This is so complex it gives CPAs headaches.

Guys selling shares in marijuana production and other private placement investments are usually promising huge returns when the venture is sold or goes public - if either ever happens. They have total say over when and if that happens, if it ever does, and over whether or not you can sell early if you need to bail out, and if so at what price.

Yes, some people make big bucks on such investments, but most lose their money.

At my age, liquidity is very important - so there is no way I'll invest in any private placement whatever. If it isn't publicly traded now I'm not interested.