Trilobites from the St. Petersburg area of Russia generally fetch high prices if complete and prepared well, meaning that reconstruction is often applied to broken specimens to give them a nice overall finish. The amount of reconstruction is very little in comparison to Moroccan trilobites which are often completely fabricated (Link).
Restoration on Russian trilobites are limited to filling in cracks from damage during extraction (the Ordovician rocks in which they are found are particularly hard so most will have some damage when found), reattaching spines and fixing or adding lost eye pieces is also not uncommon. To find large proportions of the specimens reconstructed like the cephalon are not so likely to be encountered but do occur.
Cystoids are frequently found alone and are commonly artificially attached to trilobite plates by preparers to make them more desirable. A trilobite on matrix can fetch a higher price than one out of matrix so now and again genuine specimens are attached to a new matrix block. Despite a more attractive and displayable example, further preparation is impossible and they lose all stratigraphy information if attached to matrix from a different level to that it was found in. It can be difficult to tell the difference between genuine and fake Russian trilobites by looking out for detail as they are often kept under air abrasive for too long resulting in a loss of surface texture. This aggressive preparation sometimes gives the trilobites a polished appearance and the price is reflected by this. Skilfully prepared specimens (particularly the more spiny trilobites) are far more costly and have a greater scientific value.
The trilobite slab below consists of a number of Asaphus punctatus trilobites and a cystoid on a single slab. Such proximity all on the same level could suggest an artificial arrangement so the specimen was examined under UV light. The results can clearly be seen showing up as fluorescent: 4 genuine trilobites on original matrix (slight reconstruction on the eyes and ribbing but not surprising with the extraction methods). The cystoid was added to the matrix but the 4 trilobites are in original positions. A rare specimen.