Please note: we are no law enforcement persons. We can not do anything to punish relic dealers but warn you.
Please note: we don't accuse every seller to say they are thefts. Many of these objects were stolen at World War II or at another opportunity. Many sellers probably don't even know the sale of relics is not correct according to all the cleric laws. So there are not all real criminels at Ebay for example. (Professionel dealers can be considered as misuser of the relics.)
We just want to inform you about the customs on the illegal market.
Above you see a statement of the holy see (Vatican) at Rome. The document says, holy relics can normally not be obtained by private persons. (We are waiting for an english version.)
At EBAY, private websites, flea market in Luxembourg and Belgium and otherwise there are always many relics for sale. Now you shoud think, where is the relic coming from? Answers like "got it from my grand dad" are bad, because the grand dad had to be a priest to get access to the relics of his church. But a priest should not be grand dad - isn't it.
Many peoples say they get relicsnfrom poor monasterys or private chapels. That is not allowed.
If you buy such a relic you may be involved in a crime and the relic gets lost of all the benedictions made before the theca has been sealed.
here a link to Interpol, maybe you can find objects you have seen somewhere

There is unfortunately a big dump of simonists who sell against canon law and the catechism (who says:
a:Cleric Law (CIC = codex juris canonici) forbids sale of relics of category 1 (parts of the body - hairs, bones etc. of a saint) and category 2 (personnal propriety of the saint like clothing etc.).
b:The catechism says at 2121 Simony is defined as the buying or selling of spiritual things. To Simon the magician, who wanted to buy the spiritual power he saw at work in the apostles, St. Peter responded: "Your silver perish with you, because you thought you could obtain God's gift with money!" Peter thus held to the words of Jesus: "You received without pay, give without pay." It is impossible to appropriate to oneself spiritual goods and behave toward them as their owner or master, for they have their source in God. One can receive them only from him, without payment.

There is a market with enorm stocks of holy relics that may be stolen, come from a bankrupt monasterys or a closed private chapels. This happens due to the bad financial situation so many have to make money to maintain for example the monastery or sell an old castle including the built in Chapel after having sold all the "things" that bring supplements of money.
Relic dealers have a feeling like dung flyes to use the situations of such persons in financial troubles and they may obtain wonderful relics .
If you noted what we quoted above, you know, you shall not buy anything at such guys, but what do you do if there is a sale of the skull of an holy body who lays in your church? Wouldn't it be fine to complete your saint? Law says no! What says your chest, your devotion to this saint? Do you want to let a private guy possess this relic?
We understand your doubts and maybe we can give you a little help.
Besides the sample we cited above mostly you will find smaller thecas with holy relics, mostly without documents for sometimes very cheap prices at EBAY for example (even if EBAY forbids sale of human remains). This relic may be marked with Francis, Benedict or Anthony without any more indications.
Here we may give you a little help: We possess a register with about 15'000 Saints and blesseds. As requests at the bollandists means often you have to buy the whole library, (a wonderful library for people with lots of money and willing to spend the rest of their live with hagiography) but a bit too costful for enquiries about "how much Benedicts have been canonized, whats their full name and eventual other data"!
As we possess so much data, we will give them to you for free, as a little for churches! Just send us an Email with your request and full Address, fax and Phone No. because sometimes we contact you to be sure we are giving our data to the church and not to simonists.
For privates we are not really willing to give away such data like this, because this is also a help to make better false relics. If even -privates have to write us, join a letter of recommendation of their parish, certificate of baptismal (photocopy) we will contact the parish and they have to pay for the time we spend.

These 2 pictures
revers

shows us a perfectly made false relic. It is also a fact, every holy relic coming from the Vatican has a document signed and sealed by a bishop confirming the content of the relic, kind of theca and date of manufacturation. Without these papers, your doubts are more than justified, but with the papers you may think, how the relic comes (for example) to EBAY. At EBAY you may also buy documents without relics. So you may "order" a false according to your document after that.
You see, there are hundreds of ways to offer holy relics to sellers, but considering the letter of the holy see you must know, there is always something of illegal with the "carreer" of the relic.
Some more informations about relic dealing
Join Rev. Prof. P. Meier - please click here

And if you really must collect relics - > On this Link you may buy contact relics in different presentations, in Medals, with cards etc. The trade of these cat 3 or 4 relics is legadl and it makes no difference if you use a Skull of a saint - that cant be obtained legally - or a little prayers card with such a contact relic for your veneration of a saint. And finnally prices are really very supportable. And if you want to collect holy relics, this seems the one and only way to do it for me!
Here an example:

St. Philomena Chapel
Las Vegas, NV, 89108 - US