But be careful in your wording.  A lot of times, it can come off the wrong way.  That certainly isn't the first thing I would tell a provider in your initial email.

In other words, your first sentence shouldn't be, "Can we trade services, since I have no money?"

That's no different than asking a girl that you just met in a bar:  "If I buy you this drink, can we be clear that I am doing this in the hopes of fucking you?"

barter

yes it does happen occasionally..the key is that you NEVER bring the subject up..it is a sticky subject that cheapens her view of you and it is not advisable,,if she brings it up..it is completely different..cash is always preferred..bartering means eventual trouble..

Someone always gets screwed in the end, and not in a good way

I have two policies hobbyists should live by:

1) The companions you would loan money to, are the ones who would never ask. Do not loan money to escorts.

2) Don't barter. Someone will always feel shortchanged.

If you are going to ignore my advice, and barter anyway make sure to make sure it's a fair trade for both. Also some ladies will barter, and list what they are looking for on their sites.

Some ladies have listed services that they will trade for on their websites. Some forum type hobby sites (which can't be mentioned here), have sections dedicated to barters. The ladies post what services they need. Clients post services  they provide. Services traded range from provider related services such as web design and photography, to non provider related services such as auto repair, home repair, medical, dental, cosmetic surgery, even rent.

There are a lot of considerations on both sides if getting into something like that.
1) As previous posters said, don't bring it up as a client unless she offerred first.
2) Everything has to be clear upfront as to expectations on both sides, so that it is a win win situation and one party does not end up being taken advantage of. As Ashley said, these cases can easily end up badly.
3) there is a lot of trust involved. If you are working on a lady's house, or car, or body (in the case of doctors or dentists) then you are going to know her true identity.
4) You better be a professional at what you are offering in trade. If she is looking for a photographer, she is looking for a pro photographer with a reputation and a portfolio, not some guy with a camera who likes taking pictures. If she is looking for someone to do the brakes on her BMW, then you damn well better be a certified BMW mechanic, not some guy with some tools and a Chilton manual who once changed the brake shoes on his VW Beetle in 1976.