This is what they do:
(1) They receive an order.
(2) They laugh and charge the credit card immediately.
(3) They tell you some items are back ordered without listing specifics.
(4) You don't hear from them for months and then they tell you the expensive part of your order is back ordered.
(5) Ooooops it's too late for the client to reverse credit card charges.
(6) You tell them to cancel the back ordered stuff
(7) They send you broken, used, past-the-due date stuff
(8 ) MOST IMPORTANTLY, they don't refund the difference.
(9) They don't answer phone calls.
(10) They don't reply to messages left on answering machine (most of which are full, I had to try several)
(11) They don't respond to emails.
(12) BTW they were supposedly back ordered for 4 months on DMSO... it's like the grocery store being out of eggs for 4 months.

Additional sources:
http://www.alexa.com/siteinfo/sciencelab.com#reviews
http://www.resellerratings.com/store/ScienceLab
http://www.siteadvisor.com/sites/sciencelab.com
http://www.bbb.org/houston/business-reviews/petroleum-products/science-lab-com-in-humble-tx-13007572/
http://www.sciencemadness.org/talk/viewthread.php?tid=8270
http://www.complaintsboard.com/complaints/sciencelabcom-c254656.html
http://blogs.chron.com/consumerwatch/2008/04/
http://www.ripoffreport.com/drug-manufacturers/sciencelab-com/sciencelab-com-kept-my-money-f-db4mc.htm

If you go to other forums where people may be interested in buying chemicals at some point, please pass on the warning.