This strikes me as odd. at first i thought scam, scam, scam, but maybe not. i would definitely charge for the shipping, a little bit for the packing, and it's up to you how you want to think about the sample itself. send a small one if possible.
Sending samples is not so unusual if you make ceramic tile. Actually I am surprised that so FEW people ask for samples.
I often sell the samples to the customer, and then if they place an order , (and you might want to stipulate a minimum order) , I will discount off of the order invoice some or all of the price of the samples. This works as an incentive for them to place an order.
I do charge for samples. generally I charge $10 for shipping, and $2 ea for 2X2 glaze samples... if the customer wants to see a sliced section of molding, etc, i charge based on what they want. I sell directly to customers .
generally ,unless the samples are large or extensive, i really just want to compensate for the shipping, and a little bit more.
Showrooms , architects and designers want a whole other level of samples and will often ask for a large number of samples and if they can get them for free, they will !I have done this a few times, but only when i had a standing business relationship (with an architect) who I knew would come through. otherwise , charge for your samples , or you can easily find yourself out the dollars and the work with no follow up business.
i discovered this the hard way 1. from a cruise ship line , that asked for about $300 worth of samples and never placed an order or returned samples, and 2, Sunset magazine, also asked for about $200 in samples to photograph for an article, and said they would return the pieces. So I sent them some nice tiles. they never returned the pieces, and the photos never showed up in an article. but someone somewhere has some nice free tile in their office or home, or it's in a box somewhere where no one will ever see it. never got any referrals or so much as a thank you either. learning experience!.
re reading, I see that you have found out the place is legit. if you do start a business relationship with them, you will need to make sure your shipping costs are accounted for. If they are really interested in your work,paying for shipping of a small sample should not faze them. Think about the psychology of it and try to set up good patterns early.