The usual is to do the job in Photoshop although if you have Poser 5 or later you can play with the U and V scales in in the material setting of the advanced display node set ups.

I have corrected a number of purchased tiles so I can just tile them proceduraly. Thing is I have bought 4 or 5 tiling texture sets in the market place, so-called seamless textures, only to find that yes the border has been blurred to make the texture "seamless" but that there has been no effort to supress elements in the tile that show the repeate. I can't use any of them as tiles without fixing them or I have to paint the map with them in photoshop and clone/mend to hide the repeating elements. Then there are the market place fabric tiles and wallpapers I have bought, rather than align the image to repeat properly and uniformly, instead I find that they have placed a blur or fade running through important elements, perhaps they batch procesed the tiles to be seamles with a Photoshop filter rather than editing them "by hand".

Some vendors it seems think that the blur and  fade of the tile edge make a texture "tiling" and "seamless", I don't agree... So far the vendors I have bought from have cropped tight "to protect" their samples from unauthorized use but this has also served to hide the defect of the products in all the purchases I have made, that the tile shows a pronouced repeat where it should not or a distorting repeat where the repeat should be regular such as a bouquette of flowers on a repeating wallpaper or cloth.