We tried a few things;
Self-serve making their own tickets via a contact form - they couldn't provide enough information to make it useful
Various types of contact forms, like so;
(the form on the right)
These DO work - but I would not consider this 'online booking' - this is just lead generation, you have to follow up with all of these very actively.
We also use Joomla and used a number of "appointment booking" components, especially resource booking pro and appointment booking pro -
They work - but nobody would ever use them, and, the usability on tools like that isn't great.
I tried tungle.me for quite a while in my email signature, and with online links, I even told about 10 people to go there and nobody ever got all the way through it to book something 'all the way' to a scheduled appointment.
We eventually settled on just using various types of contact forms, with and without captchas, etc - when you get a lot of web traffic - the spam gets a little crazy.
One thing you should be doing is building multiple pages on your site, and multiple contact forms, and point one adwords campaign at one contact form -
setup funnels in google analytics to see those pages, tie them to the campaigns, and all the way through to the SEPARATE thank you pages for each form.
You'll be able to measure campaigns spend, and leads - unless they stop and call you.
I didn't spend the time to get properly sophisticated to show different tracking phone numbers on each contact form - because I thought enough people would start clicking around the site and the phone numbers would be generic again once they left the page.
IF you want to build some squeeze pages, so they can't click around, and you can use tracking phone numbers, it would give you some awesome feedback - I always thought a squeeze page would be the next thing I'll try in optimizing my adwords - but I can't figure out how to spend more than like $300/month in my market - so not sure I want to put a ton of effort in to that right now.
I can tell you this, if there was enough traffic to get that spend up to like $1000/month I would be building a set of squeeze pages right now.
Troy - RepairShopr