Mostly, it's their bodies, in chunks of 60-90 minutes, in the form of a massage (sorry, I meant to say "sacred ritual"). Sometimes, it's a book or a workshop.
To some degree, the part about having something to sell goes for everyone. We all sell off our precious life time to be able to pay the rent. We all dish out a white lie now and then, keep our opinions to ourselves for peace and money. It's a globalized capitalist society, and it fosters hypocrisy, dressing up for the occasion, producing a blinding light of marketing for ourselves, seeing ourselves as the product.
More to the point, it definitely goes for me and this blog. While I don't sell you anything for money (I have a decent day job to pay my rent), I do try to get you to read my blog, and I want you to like it (and by extension, I want you to like me). Not for monetary reasons, but for that most basic reason every blogger has: self-expression and ego-stroking.
The degree to which I am trying to get you to do something determines my degree of dishonesty. I will, occasionally, post on someone else's blog to leave some more or less useful, more or less witty comment - and I do this, of course, in the hope that someone will click on the link and land here.
As some may admit, trying to get you to spend a few minutes perusing my blog is less problematic than trying to get you separated from noteworthy parts of your money.
Those trying to sell their tantra massage sessions, who have become dependent upon this source of income, will obviously go longer distances to achieve their goal. They will spill out article after article, tweet after blog posting after facebook status message, to get you to read their site and then, hopefully, book a session. Those articles won't all be glimmering with bright and intelligent revelations. They will just rehash "authentic", i.e. archaic and often oddly conservative "tantric" teachings that, strangely, always seem to burn down to the same three points: breathe deep, take your time, enjoy male/female polarity. Depending on the author, they will be more or less kinky, more or less religious, more or less this-or-that. And they will always be filled to the brim with cute, sweet, esoteric jargon.
There is good reason for that: On the most general level, which is the only one that will bring in the customers (sorry, I meant to say "acolytes"), there is not a lot more to say about tantra. It is really that simple. The levels at which it gets interesting are those of deep personal experience, where it is often hard to even express your meaning coherently, where it is a question of decency and safety not to reveal to much, and prohibitively hard to create soundbites for the market.
The irony is that tantra is about being present, mindful, in the moment, and spiritual guidance might imply strength of character and lack of ego on part of the giver (or "goddess", as they seem to customarily call themselves these days). You can't be present and in the moment while you're meditating how best to drive people to your site, and I fail to see a lot of egoless enlightenment in lying through your teeth to sell me some sex, or wrapping up sexual services in fluffy religious jargon.
While we're all hypocritical in principle, while we're all guilty and shouldn't judge each other, there are different degrees of ugliness to our actions. Maybe my biggest lie is to my boss, yours is to your husband - it's not about the person, but about the action.
What I'm saying is, take it for what it is - a fun little roleplay for spicing up the action. Don't expect that a "tantra goddess" can give you any insight, healing, or spiritual guidance. Decide whether the relaxation and fun that can be gathered through a good "tantric massage" is worth your money. In my experience, it will probably be better than your run-off-the-mill pay-by-the-hour sex, even if it's not exactly a religious revelation.
In short, don't believe the hype.